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• Divide people into teams for most satisfaction

  - by Jweede

  Just a curiosity question. Remember when in class groupwork the professor would divide people up into groups of a certain number (n)? Some of my professors would take a list of n people one wants to work with and n people one doesn't want to work with from each student, and then magically turn out groups of n where students would be matched up with people they prefer and avoid working with people they don't prefer. To me this algorithm sounds a lot like a Knapsack problem, but I thought I would ask around about what your approach to this sort of problem would be.

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• Randomly generating sequence of ints in a specific range

  - by vvv

  Hi, I am unsure how to put this and my math skills aren't that strong. But here's what I need. I want to generate a list of all the 16bit integers (0-65535). But everytime I do so I want to seed the algorithm randomly that each time the list starts with a different integer and all the subsequent integers will be generated once but also in random order. small example (1-5): ... 1, 5, 3, 2, 4 4, 3, 1, 5, 2 2, 1, 4, 5, 3 ... Any help?

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• Creative Technical Interview Questions for Developers

  - by John Shedletsky

  I do a good number of in-person technical interviews for new developers. I like to ask technical questions where I ask people to either code something up or develop an algorithm to solve a task. I feel my current repertoire is uninspired. In my opinion, the ideal interview question has these qualities: Multiple solutions, where some are obviously better than others, and some that involve subtle trade-offs (discussing tradeoffs is a good way to gauge someone's experience, in my opinion). Novelty - asking the "insert this element into a linked list" question is only good for weeding out people who never did their homework. Elegant - I like questions where the core problem isn't hidden in a lot of details. Everyone should be able to understand the problem, even if everyone can't solve it on the whiteboard. Elegant questions are difficult without involving undue amounts of "domain knowledge" or getting too narrow. Have you been on either side of an interview where someone (maybe you!) asked a particularly good programming or algorithms question?

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• Arrange 0's & 1's in a array

  - by Ganesh M

  This is one of an interview question which I had recently. I would like to know others perception of approach for this problem. Question: You are given a structure which holds an employee details with two elements as int Deptartment and string Name. struct Employee { string Name; int Dept; } You are given details of N Employees among which there are N/2 employees Dept are 0's and N/2 employees dept are 1's arranged in some random order. You need to sort the employee details based on their Dept value and it should be stable i.e., the order of 1s and 0s in the original record should be maintained. For example, given the following sample data: Name Dept X1 0 X2 1 X3 0 X4 1 X5 0 after sorting the result should be: Name Dept X2 1 X4 1 X1 0 X3 0 X5 0 The algorithm should be stable and the complexity should be o(N), with constant space for additional variables (which means sorting should be done in-place).

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• Getting facts from documents

  - by dotnetdev

  Hi, I want to be able to get all the facts from webpages. But these have to be related to coding, and not, for example, about something irrelevant. For example: The Engine renders at a decent speed. May be a fact but is not what I am interested in. If the same article states: A class is a reference type. (This is C#) Then I am interested in that as it is coding related. Has an algorithm like this ever been done? How hard would this be? I'm thinking AI would come into play here. Any advice sought. Thanks

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• How do I pick the most beneficial combination of items from a set of items?

  - by Chu

  I'm designing a piece of a game where the AI needs to determine which combination of armor will give the best overall stat bonus to the character. Each character will have about 10 stats, of which only 3-4 are important, and of those important ones, a few will be more important than the others. Armor will also give a boost to 1 or all stats. For example, a shirt might give +4 to the character's int and +2 stamina while at the same time, a pair of pants may have +7 strength and nothing else. So let's say that a character has a healthy choice of armor to use (5 pairs of pants, 5 pairs of gloves, etc.) We've designated that Int and Perception are the most important stats for this character. How could I write an algorithm that would determine which combination of armor and items would result in the highest of any given stat (say in this example Int and Perception)?

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• Find the period of over speed ?

  - by Vimvq1987

  Just something interesting come in my mind. Assume that we have a table (in SQL Server) like this: Location Velocity Time What is the best way to determine over speed periods (speed barrier is defined) ? My first idea was loading the table into an array, and then iterate over array to find these periods: (Pseudo C# code) bool isOverSpeed = false; for (int i =0;i<arr.Length;i++) { if (!isOverSpeed) if (arr[i].Velocity > speedBarrier) { #insert the first record into another array. isOverSpeed = true; } if(isOverSpeed) if (arr[i].Velocity < speedBarrier) { #insert the record into that array isOverSpeed = false; } } It works, but somewhat "not very effectively". Is there a "smarter" way, such as a T-SQL query or another algorithm to do this?

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• Having trouble getting GET variables from url.

  - by mchl

  Hey everyone, I'm having trouble with this algorithm to extract the get variables from a url and print them each on a new line like: x=y z=hello etc. but instead it prints a seemingly random section of the url with no newlines to the file. There must be a logic error of some kind but i just can't spot it. for(i_m=0;i_m<len_m;i_m++) { if(var_m[i_m]=='&') { fwrite(var_m+offset_m, 1, amp_m, echo_out); fputc('\n',echo_out); offset_m+=amp_m; amp_m=0; } amp_m++; } any help appreciated.

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• question abouut string sort

  - by davit-datuashvili

  i have question from programming pearls problem is following show how to use lomuto's partitioning scheme to sort varying length bit strings in time proportional to the sum oof their length and algorithm is following each record in x[0..n-1] has an integer length and pointer to the array bit[0..length-1] code void bsort(l,u,depth){ if (l>=u) return; for (int i=l;i<u;i++) if (x[i].length<depth) swap(i,l++); m=l; if (x[i].bit[depth] ==0) swap(i,m++); bsort(l,m-1,depth+1); bsort(m,u,depth+1); please help me i need following things 1. how this algorith works 2.how implement in java?

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• Implementing "select distinct ... from ..." over a list of Python dictionaries

  - by daveslab

  Hi folks, Here is my problem: I have a list of Python dictionaries of identical form, that are meant to represent the rows of a table in a database, something like this: [ {'ID': 1, 'NAME': 'Joe', 'CLASS': '8th', ... }, {'ID': 1, 'NAME': 'Joe', 'CLASS': '11th', ... }, ...] I have already written a function to get the unique values for a particular field in this list of dictionaries, which was trivial. That function implements something like: select distinct NAME from ... However, I want to be able to get the list of multiple unique fields, similar to: select distinct NAME, CLASS from ... Which I am finding to be non-trivial. Is there an algorithm or Python included function to help me with this quandry? Before you suggest loading the CSV files into a SQLite table or something similar, that is not an option for the environment I'm in, and trust me, that was my first thought.

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• Permutations with extra restrictions

  - by Full Decent

  I have a set of items, for example: {1,1,1,2,2,3,3,3}, and a restricting set of sets, for example {{3},{1,2},{1,2,3},{1,2,3},{1,2,3},{1,2,3},{2,3},{2,3}. I am looking for permutations of items, but the first element must be 3, and the second must be 1 or 2, etc. One such permutation that fits is: {3,1,1,1,2,2,3} Is there an algorithm to count all permutations for this problem in general? Is there a name for this type of problem? For illustration, I know how to solve this problem for certain types of "restricting sets". Set of items: {1,1,2,2,3}, Restrictions {{1,2},{1,2,3},{1,2,3},{1,2},{1,2}}. This is equal to 2!/(2-1)!/1! * 4!/2!/2!. Effectively permuting the 3 first, since it is the most restrictive and then permuting the remaining items where there is room.

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• complexity of algorithms

  - by davit-datuashvili

  i have question what is complexity of this algorithm public class smax{ public static void main(String[]args){ int b[]=new int[11]; int a[]=new int[]{4,9,2,6,8,7,5}; for (int i=0;i int m=0; while (m int k=a[0]; for (int i=0;i k && b[a[i]]!=1){ b[a[i]]=1; } } m++; } for (int i=0;i for (int j=0;j //result=2 4 5 6 7 8 9 } } ?

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• Print all ways to sum n integers so that they total a given sum.

  - by noghead

  Im trying to come up with an algorithm that will print out all possible ways to sum N integers so that they total a given value. Example. Print all ways to sum 4 integers so that they sum up to be 5. Result should be something like: 5 0 0 0 4 1 0 0 3 2 0 0 3 1 1 0 2 3 0 0 2 2 1 0 2 1 2 0 2 1 1 1 1 4 0 0 1 3 1 0 1 2 2 0 1 2 1 1 1 1 3 0 1 1 2 1 1 1 1 2

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• How to get it working in O(n)?

  - by evermean

  I came across an interview task/question that really got me thinking ... so here it goes: You have an array A[N] of N numbers. You have to compose an array Output[N] such that Output[i] will be equal to multiplication of all the elements of A[N] except A[i]. For example Output[0] will be multiplication of A[1] to A[N-1] and Output[1] will be multiplication of A[0] and from A[2] to A[N-1]. Solve it without division operator and in O(n). I really tried to come up with a solution but I always end up with a complexity of O(n^2). Perhaps the is anyone smarter than me who can tell me an algorithm that works in O(n) or at least give me a hint...

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• Versioned RDF store

  - by Mat

  Let me try rephrasing this: I am looking for a robust RDF store or library with the following features: Named graphs, or some other form of reification. Version tracking (probably at the named graph level). Privacy between groups of users, either at named graph or triple level. Human-readable data input and output, e.g. TriG parser and serialiser. I've played with Jena, Sesame, Boca, RDFLib, Redland and one or two others some time ago but each had its problems. Have any improved in the above areas recently? Can anything else do what I want, or is RDF not yet ready for prime-time? Reading around the subject a bit more, I've found that: Jena, nothing further Sesame, nothing further Boca does not appear to be maintained any more and seems only really designed for DB2. OpenAnzo, an open-source fork, appears more promising. RDFLib, nothing further Redland, nothing further Talis Platform appears to support changesets (wiki page and reference in Kniblet Tutorial Part 5) but it's a hosted-only service. Still may look into it though. SemVersion sounded promising, but appears to be stale.

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• retrieve events where uid is the creator and application id is the admin - Facebook API

  - by Anup Parekh

  I would like to know if there is a Facebook API call to retrieve the events (eids) for all the events a user has created using my facebook connect application. The events are created using the following REST api call: https://api.facebook.com/method/events.create?event_info=' . $e_i . '&access_token=' . $cookie['access_token'] $e_i is the event info array where the 'host' value is set to 'Me' as follows $event_info['host'] = 'Me'; On Facebook events under the "Created by:" section it lists "My user name,Application Name", I presume this is because I am the creator and the application is the admin as stated in the REST api documentation http://developers.facebook.com/docs/reference/rest/events.create/ Unfortunately I cannot seem to find out how (neither REST nor GPRAPH API) to return a list of events where I am the creator and the application is the admin as in the above scenario. If this is possible I would really appreciate some assistance with how it is done. So far I have tried: REST API events.get using uid=application_id. This only returns events created by the application not those including the user who created them GRAPH API https://graph.facebook.com/me/events?fields=owner&access_token=... this returns all the events for 'me' but not where the application is also the admin. It seems strange that there's no reference to the linkage between the event creator and the event admin through the API but in Facebook it is able to pull both and display them on the event details.

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• Facebook API - delete status

  - by Simon R

  In PHP, I'm using curl to send a delete to the fb graph api - and yet I'm getting the following error; {"error":{"type":"GraphMethodException","message":"Unsupported delete request."}} The code I'm using is; $ch = curl_init("https://graph.facebook.com/" . $status_id . ""); curl_setopt($ch, CURLOPT_VERBOSE, 1); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); curl_setopt($ch, CURLOPT_HEADER, 0); curl_setopt($ch, CURLOPT_TIMEOUT, 120); curl_setopt($ch, CURLOPT_POST, 1); curl_setopt($ch, CURLOPT_POSTFIELDS, $query); curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "DELETE"); curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 1); curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); curl_setopt($ch, CURLOPT_CAINFO, NULL); curl_setopt($ch, CURLOPT_CAPATH, NULL); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 0); $result = curl_exec($ch); echo $result; $query contains the access token.

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• How can my facebook application post message to a wall?

  - by Thomas Dekiere

  i already found out how to post something to a wall with the graph api on behalf of the facebook user. But now i want to post something in the name of my application. Here is how i'm trying to do this: protected void btn_submit_Click(object sender, EventArgs e) { Dictionary<string, string> data = new Dictionary<string, string>(); data.Add("message", "Testing"); // i'll add more data later here (picture, link, ...) data.Add("access_token", FbGraphApi.getAppToken()); FbGraphApi.postOnWall(ConfigSettings.getFbPageId(), data); } FbGraphApi.getAppToken() // ... private static string graphUrl = "https://graph.facebook.com"; //... public static string getAppToken() { MyWebRequest req = new MyWebRequest(graphUrl + "/" + "oauth/access_token?type=client_cred&client_id=" + ConfigSettings.getAppID() + "&client_secret=" + ConfigSettings.getAppSecret(), "GET"); return req.GetResponse().Split('=')[1]; } FbGraphApi.postOnWall() public static void postOnWall(string id, Dictionary<string,string> args) { call(id, "feed", args); } FbGraphApi.call() private static void call(string id, string method, Dictionary<string,string> args ) { string data = ""; foreach (KeyValuePair<string, string> arg in args) { data += arg.Key + "=" + arg.Value + "&"; } MyWebRequest req = new MyWebRequest(graphUrl +"/" + id + "/" + method, "POST", data.Substring(0, data.Length - 1)); req.GetResponse(); // here i get: "The remote server returned an error: (403) Forbidden." } Does anyone see where this i going wrong? I'm really stuck on this. Thanks!

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• Trend analysis using iterative value increments

  - by Dave Jarvis

  We have configured iReport to generate the following graph: The real data points are in blue, the trend line is green. The problems include: Too many data points for the trend line Trend line does not follow a Bezier curve (spline) The source of the problem is with the incrementer class. The incrementer is provided with the data points iteratively. There does not appear to be a way to get the set of data. The code that calculates the trend line looks as follows: import java.math.BigDecimal; import net.sf.jasperreports.engine.fill.*; /** * Used by an iReport variable to increment its average. */ public class MovingAverageIncrementer implements JRIncrementer { private BigDecimal average; private int incr = 0; /** * Instantiated by the MovingAverageIncrementerFactory class. */ public MovingAverageIncrementer() { } /** * Returns the newly incremented value, which is calculated by averaging * the previous value from the previous call to this method. * * @param jrFillVariable Unused. * @param object New data point to average. * @param abstractValueProvider Unused. * @return The newly incremented value. */ public Object increment( JRFillVariable jrFillVariable, Object object, AbstractValueProvider abstractValueProvider ) { BigDecimal value = new BigDecimal( ( ( Number )object ).doubleValue() ); // Average every 10 data points // if( incr % 10 == 0 ) { setAverage( ( value.add( getAverage() ).doubleValue() / 2.0 ) ); } incr++; return getAverage(); } /** * Changes the value that is the moving average. * @param average The new moving average value. */ private void setAverage( BigDecimal average ) { this.average = average; } /** * Returns the current moving average average. * @return Value used for plotting on a report. */ protected BigDecimal getAverage() { if( this.average == null ) { this.average = new BigDecimal( 0 ); } return this.average; } /** Helper method. */ private void setAverage( double d ) { setAverage( new BigDecimal( d ) ); } } How would you create a smoother and more accurate representation of the trend line?

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• parsing of mathematical expressions

  - by gcc

  (in c90) (linux) input: sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: cos(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B)) /*max lenght of formula is 250 characters*/ a b /*there are values for a,b,c,d */ c /*each variable with set of floating numbers*/ d As you can see infix formula in the input depends on user. My program will take a formula and n-tuples value. Then it calculate the results for each value of a,b,c and d. If you wonder I am saying ;outcome of program is graph. /sometimes,I think i will take input and store in string. then another idea is arise " I should store formula in the struct" but i don't know how I can construct the code on the base of structure./ really, I don't know way how to store the formula in program code so that I can do my job. can you show me? /* a,b,c,d is letters cos,sin,sqrt,ln is function*/

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• Non recursive way to position a genogram in 2D points for x axis. Descendant are below

  - by Nassign

  I currently was tasked to make a genogram for a family consisting of siblings, parents with aunts and uncles with grandparents and greatgrandparents for only blood relatives. My current algorithm is using recursion. but I am wondering how to do it in non recursive way to make it more efficient. it is programmed in c# using graphics to draw on a bitmap. Current algorithm for calculating x position, the y position is by getting the generation number. public void StartCalculatePosition() { // Search the start node (The only node with targetFlg set to true) Person start = null; foreach (Person p in PersonDic.Values) { if (start == null) start = p; if (p.Targetflg) { start = p; break; } } CalcPositionRecurse(start); // Normalize the position (shift all values to positive value) // Get the minimum value (must be negative) // Then offset the position of all marriage and person with that to make it start from zero float minPosition = float.MaxValue; foreach (Person p in PersonDic.Values) { if (minPosition > p.Position) { minPosition = p.Position; } } if (minPosition < 0) { foreach (Person p in PersonDic.Values) { p.Position -= minPosition; } foreach (Marriage m in MarriageList) { m.ParentsPosition -= minPosition; m.ChildrenPosition -= minPosition; } } } /// <summary> /// Calculate position of genogram using recursion /// </summary> /// <param name="psn"></param> private void CalcPositionRecurse(Person psn) { // End the recursion if (psn.BirthMarriage == null || psn.BirthMarriage.Parents.Count == 0) { psn.Position = 0.0f; if (psn.BirthMarriage != null) { psn.BirthMarriage.ParentsPosition = 0.0f; psn.BirthMarriage.ChildrenPosition = 0.0f; } CalculateSiblingPosition(psn); return; } // Left recurse if (psn.Father != null) { CalcPositionRecurse(psn.Father); } // Right recurse if (psn.Mother != null) { CalcPositionRecurse(psn.Mother); } // Merge Position if (psn.Father != null && psn.Mother != null) { AdjustConflict(psn.Father, psn.Mother); // Position person in center of parent psn.Position = (psn.Father.Position + psn.Mother.Position) / 2; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else { // Single mom or single dad if (psn.Father != null) { psn.Position = psn.Father.Position; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else if (psn.Mother != null) { psn.Position = psn.Mother.Position; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else { // Should not happen, checking in start of function } } // Arrange the siblings base on my position (left younger, right older) CalculateSiblingPosition(psn); } private float GetRightBoundaryAncestor(Person psn) { float rPos = psn.Position; // Get the rightmost position among siblings foreach (Person sibling in psn.Siblings) { if (sibling.Position > rPos) { rPos = sibling.Position; } } if (psn.Father != null) { float rFatherPos = GetRightBoundaryAncestor(psn.Father); if (rFatherPos > rPos) { rPos = rFatherPos; } } if (psn.Mother != null) { float rMotherPos = GetRightBoundaryAncestor(psn.Mother); if (rMotherPos > rPos) { rPos = rMotherPos; } } return rPos; } private float GetLeftBoundaryAncestor(Person psn) { float rPos = psn.Position; // Get the rightmost position among siblings foreach (Person sibling in psn.Siblings) { if (sibling.Position < rPos) { rPos = sibling.Position; } } if (psn.Father != null) { float rFatherPos = GetLeftBoundaryAncestor(psn.Father); if (rFatherPos < rPos) { rPos = rFatherPos; } } if (psn.Mother != null) { float rMotherPos = GetLeftBoundaryAncestor(psn.Mother); if (rMotherPos < rPos) { rPos = rMotherPos; } } return rPos; } /// <summary> /// Check if two parent group has conflict and compensate on the conflict /// </summary> /// <param name="leftGroup"></param> /// <param name="rightGroup"></param> public void AdjustConflict(Person leftGroup, Person rightGroup) { float leftMax = GetRightBoundaryAncestor(leftGroup); leftMax += 0.5f; float rightMin = GetLeftBoundaryAncestor(rightGroup); rightMin -= 0.5f; float diff = leftMax - rightMin; if (diff > 0.0f) { float moveHalf = Math.Abs(diff) / 2; RecurseMoveAncestor(leftGroup, 0 - moveHalf); RecurseMoveAncestor(rightGroup, moveHalf); } } /// <summary> /// Recursively move a person and all his/her ancestor /// </summary> /// <param name="psn"></param> /// <param name="moveUnit"></param> public void RecurseMoveAncestor(Person psn, float moveUnit) { psn.Position += moveUnit; foreach (Person siblings in psn.Siblings) { if (siblings.Id != psn.Id) { siblings.Position += moveUnit; } } if (psn.BirthMarriage != null) { psn.BirthMarriage.ChildrenPosition += moveUnit; psn.BirthMarriage.ParentsPosition += moveUnit; } if (psn.Father != null) { RecurseMoveAncestor(psn.Father, moveUnit); } if (psn.Mother != null) { RecurseMoveAncestor(psn.Mother, moveUnit); } } /// <summary> /// Calculate the position of the siblings /// </summary> /// <param name="psn"></param> /// <param name="anchor"></param> public void CalculateSiblingPosition(Person psn) { if (psn.Siblings.Count == 0) { return; } List<Person> sibling = psn.Siblings; int argidx; for (argidx = 0; argidx < sibling.Count; argidx++) { if (sibling[argidx].Id == psn.Id) { break; } } // Compute position for each brother that is younger that person int idx; for (idx = argidx - 1; idx >= 0; idx--) { sibling[idx].Position = sibling[idx + 1].Position - 1; } for (idx = argidx + 1; idx < sibling.Count; idx++) { sibling[idx].Position = sibling[idx - 1].Position + 1; } }

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• How can I tweak this A* search pathfinding algorithm to handle different terrain movement values?

  - by user422318

  I'm creating a 2D map-based action game with similar interaction design as Diablo II. In other words, the player clicks around a map to move their player. I just finished player movement and am moving on to pathfinding. In the game, enemies should charge the player's character. There are also five different terrain types that give different movement bonuses. I want the AI to take advantage of these terrain bonuses as they try to reach the player. I was told to check out the A* search algorithm (http://en.wikipedia.org/wiki/A*_search_algorithm). I'm doing this game in HTML5 and JavaScript, and found a version in JavaScript: http://www.briangrinstead.com/blog/astar-search-algorithm-in-javascript I'm trying to figure out how to tweak it though. Below are my ideas about what I need to change. What else do I need to worry about? When I create a graph, I will need to initialize the 2D array I pass in passed on with a traversal of a map that corresponds to the different terrain types. in graph.js: "GraphNodeType" definition needs to be modified to handle the 5 terrain types. There will be no walls. in astar.js: The g and h scoring will need to be modified. How should I do this? in astar.js: isWall() should probably be removed. My game doesn't have walls. in astar.js: I'm not sure what this is. I think it indicates a node that isn't valid to be processed. When would this happen, though? At a high level, how do I change this algorithm from "oh, is there a wall there?" to "will this terrain get me to the player faster than the terrain around me?" Because of time, I'm also debating reusing my Bresenham algorithm for the enemies. Unfortunately, the different terrain movement bonuses won't be used by the AI, which will make the game suck. :/ I'd really like to have this in for the prototype, but I'm not a developer by trade nor am I a computer scientist. :D If you know of any code that does what I'm looking for, please share! Sanity check tips for this are also appreciated.

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• Applying the Knuth-Plass algorithm (or something better?) to read two books with different length and amount of chapters in parallel

  - by user147133

  I have a Bible reading plan that covers the whole Bible in 180 days. For the most of the time, I read 5 chapters in the Old Testament and 1 or 2 (1.5) chapters in the New Testament each day. The problem is that some chapters are longer than others (for example Psalm 119 which is 7 times longer than a average chapter in the Bible), and the plan I'm following doesn't take that in count. I end up with some days having a lot more to read than others. I thought I could use programming to make myself a better plan. I have a datastructure with a list of all chapters in the bible and their length in number of lines. (I found that the number of lines is the best criteria, but it could have been number of verses or number of words as well) I then started to think about this problem as a line wrap problem. Think of a chapter like a word, a day like a line and the whole plan as a paragraph. The "length" of a word (a chapter) is the number of lines in that chapter. I could then generate the best possible reading plan by applying a simplified Knuth-Plass algorithm to find the best breakpoints. This works well if I want to read the Bible from beginning to end. But I want to read a little from the new testament each day in parallel with the old testament. Of course I can run the Knuth-Plass algorithm on the Old Testament first, then on the New Testament and get two separate plans. But those plans merged is not a optimal plan. Worst-case days (days with extra much reading) in the New Testament plan will randomly occur on the same days as the worst-case days in the Old Testament. Since the New Testament have about 180*1.5 chapters, the plan is generally to read one chapter the first day, two the second, one the third etc... And I would like the plan for the Old Testament to compensate for this alternating length. So I will need a new and better algorithm, or I will have to use the Knuth-Plass algorithm in a way that I've not figured out. I think this could be a interesting and challenging nut for people interested in algorithms, so therefore I wanted to see if any of you have a good solution in mind.

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• faster implementation of sum ( for Codility test )

  - by Oscar Reyes

  How can the following simple implementation of sum be faster? private long sum( int [] a, int begin, int end ) { if( a == null ) { return 0; } long r = 0; for( int i = begin ; i < end ; i++ ) { r+= a[i]; } return r; } EDIT Background is in order. Reading latest entry on coding horror, I came to this site: http://codility.com which has this interesting programming test. Anyway, I got 60 out of 100 in my submission, and basically ( I think ) is because this implementation of sum, because those parts where I failed are the performance parts. I'm getting TIME_OUT_ERROR's So, I was wondering if an optimization in the algorithm is possible. So, no built in functions or assembly would be allowed. This my be done in C, C++, C#, Java or pretty much in any other. EDIT As usual, mmyers was right. I did profile the code and I saw most of the time was spent on that function, but I didn't understand why. So what I did was to throw away my implementation and start with a new one. This time I've got an optimal solution [ according to San Jacinto O(n) -see comments to MSN below - ] This time I've got 81% on Codility which I think is good enough. The problem is that I didn't take the 30 mins. but around 2 hrs. but I guess that leaves me still as a good programmer, for I could work on the problem until I found an optimal solution: Here's my result. I never understood what is those "combinations of..." nor how to test "extreme_first"

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• Getting the submatrix with maximum sum?

  - by guirgis

  With the help of the Algorithmist and Larry and a modification of Kadane's Algorithm, here is my solution: int dim = matrix.length; //computing the vertical prefix sum for columns int[][] ps = new int[dim][dim]; for (int i = 0; i < dim; i++) { for (int j = 0; j < dim; j++) { if (j == 0) { ps[j][i] = matrix[j][i]; } else { ps[j][i] = matrix[j][i] + ps[j - 1][i]; } } } int maxSoFar = 0; int min , subMatrix; //iterate over the possible combinations applying Kadane's Alg. //int toplefti =0, topleftj=0, bottomrighti=0, bottomrightj=0; for (int i = 0; i < dim; i++) { for (int j = i; j < dim; j++) { min = 0; subMatrix = 0; for (int k = 0; k < dim; k++) { if (i == 0) { subMatrix += ps[j][k]; } else { subMatrix += ps[j][k] - ps[i-1][k]; } if(subMatrix < min){ min = subMatrix; } if((subMatrix - min) > maxSoFar){ maxSoFar = subMatrix - min; } } } } The only problem left is to determine the submatrix elements, i mean the top left and the bottom right corners. I managed to do this in one dimensional case. Any suggestions?

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