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• Why increase pointer by two while finding loop in linked list, why not 3,4,5?

  - by GG

  I had a look at question already which talk about algorithm to find loop in a linked list. I have read Floyd's cycle-finding algorithm solution, mentioned at lot of places that we have to take two pointers. One pointer( slower/tortoise ) is increased by one and other pointer( faster/hare ) is increased by 2. When they are equal we find the loop and if faster pointer reaches null there is no loop in the linked list. Now my question is why we increase faster pointer by 2. Why not something else? Increasing by 2 is necessary or we can increase it by X to get the result. Is it necessary that we will find a loop if we increment faster pointer by 2 or there can be the case where we need to increment by 3 or 5 or x.

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• Is there a way to define a List<> of two elements string array?

  - by Alexander Prokofyev

  I want to build two-dimentional array of strings where length of one dimention is 2. Similar to this string[,] array = new string[,] { {"a", "b"}, {"c", "d"}, {"e", "f"}, {"g", "h"} } Doing List<string[]> list = new List<string[]>(); list.Add(new string[2] {"a", "b"}); list.Add(new string[2] {"c", "d"}); list.Add(new string[2] {"e", "f"}); list.Add(new string[2] {"g", "h"}); list.ToArray(); gives me string[][] but not string[,] array. Just curious, is there some trick to build dynamically string[,] array somehow?

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• [BST] Deletion procedure

  - by Metz

  Hi all. Consider the deletion procedure on a BST, when the node to delete has two children. Let's say i always replace it with the node holding the minimum key in its right subtree. The question is: is this procedure commutative? That is, deleting x and then y has the same result than deleting first y and then x? I think the answer is no, but i can't find a counterexample, nor figure out any valid reasoning. Thank you. EDIT: Maybe i've got to be clearer. Consider the transplant(node x, node y) procedure: it replace x with y (and its subtree). So, if i want to delete a node (say x) which has two children i replace it with the node holding the minimum key in its right subtree: y = minimum(x.right) transplant(y, y.right) // extracts the minimum (it doesn't have left child) y.right = x.right y.left = x.left transplant(x,y) The question was how to prove the procedure above is not commutative.

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• How do I output the preorder traversal of a tree given the inorder and postorder tranversal?

  - by user342580

  Given the code for outputing the postorder traversal of a tree when I have the preorder and the inorder traversal in an interger array. How do I similarily get the preorder with the inorder and postorder array given? void postorder( int preorder[], int prestart, int inorder[], int inostart, int length) { if(length==0) return; //terminating condition int i; for(i=inostart; i<inostart+length; i++) if(preorder[prestart]==inorder[i])//break when found root in inorder array break; postorder(preorder, prestart+1, inorder, inostart, i-inostart); postorder(preorder, prestart+i-inostart+1, inorder, i+1, length-i+inostart-1); cout<<preorder[prestart]<<" "; } Here is the prototype for preorder() void preorder( int inorderorder[], int inostart, int postorder[], int poststart, int length)

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• algorithm - How to sort a 0/1 array with 2n/3 comparisons?

  - by Jackson Tale

  In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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• about Sorting Algorithms

  - by matin1234

  Hi I want to know that we always use Sorting algorithm like (Insertion Sort or Merge Sort,...) just for lists and arrays?? and we do not use these algorithms for stack or queue ??? thanks

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• Given a 1TB data set on disk with around 1KB per data record, how can I find duplicates using 512MB

  - by user288609

  There is 1TB data on a disk with around 1KB per data record. How to find duplicates using 512MB RAM and infinite disk space?

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• two HashMap iteration

  - by user431276

  I have two HashMaps and I can iterate both hashmaps with following code Iterator it = mp.entrySet().iterator(); while (it.hasNext()) { Map.Entry pairs = (Map.Entry)it.next(); String firstVal = pairs.getValue(); } Iterator it2 = mp2.entrySet().iterator(); while (it2.hasNext()) { Map.Entry pairs2 = (Map.Entry)it.next(); String SecondVal = pairs2.getValue(); } myFunction(firstVal, SecondVal) Is there anyway to iterate two hashmaps at the same time without using two loops? Currently, I have a method that accepts two parameters and each parameter value is stored in first and second hashmap. I have to iterate first hash then second to get values. I think there must be a good way to do it but I don't know :( P.S: there could be some errors in above code as this is just an example to explain my problem. Each iterator is a method in original program and accept one parameter. I couldn't copy past real time functions as they are HUGE !

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• Why does dynamic array always double by a factor of 2?

  - by Phoenix

  I was wondering how does one decide the resizing factor by which dynamic array resizes ? On wikipedia and else where I have always seen the number of elements being increased by a factor of 2? Why 2? Why not 3? how does one decide this factor ? IF it is language dependent I would like to know this for Java.

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• Java data structure suggestion.

  - by techoverflow

  Hi folks, I am a newbie in this field so please excuse my silly mistakes :) So the issue I am facing is: On my webpage, I am displaying a table. For now my issue is concerned with three columns of the table. First is : Area Code Second is : Zone Code Third is: Value The relationship between these three is: 1 Area Code has 6 different Zone code's and all those 6 Zone codes have corresponding "Value" I need a data structer that would give me the flexibility to get a "Value" for a Zone code, which falls under a particular Area code. I have the same zone codes for all the Area codes: Zone codes are: 111, 222, 333, 444, 555, 666 After surfing your stackoverflow, I thought I can go with this structure: Map<Integer, Map<Integer, Double>> retailPrices = new HashMap<Integer, Map<Integer, Double>>(); Map<Integer, Double> codes = new HashMap<Integer, Double>(); where reatailPrices would hold an Area Code and a Map of Zone code as Key and "Value" as Value. but when I am trying to populate this through a SQL resultset, I am getting the following error: The method put(Integer, Map<Integer,Double>) in the type Map is not applicable for the arguments (Integer, Double) on line: `while(oResult.next()) retailPrices.put((new Integer(oResult.getString("AREA"))), (pegPlPrices.put(new Integer(oResult.getString("ZONE_CODE")), new Double(oResult.getString("VALUE"))))); }` please help me figure out this problem. Am I following the right approach?

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• Multidimensional data structure?

  - by Austin Truong

  I need a multidimensional data structure with a row and a column. Must be able to insert elements any location in the data structure. Example: {A , B} I want to insert C in between A and B. {A, C, B}. Dynamic: I do not know the size of the data structure. Another example: I know the [row][col] of where I want to insert the element. EX. insert("A", 1, 5), where A is the element to be inserted, 1 is the row, 5 is the column. EDIT I want to be able to insert like this. static void Main(string[] args) { Program p = new Program(); List<string> list = new List<string>(); list.Insert(1, "HELLO"); list.Insert(5, "RAWR"); for (int i = 0; i < list.Count; i++) { Console.WriteLine(list[i]); } Console.ReadKey(); } And of course this crashes with an out of bounds error. So in a sense I will have a user who will choose which ROW and COL to insert the element to.

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• data structure for counting frequencies in a database table-like format

  - by user373312

  i was wondering if there is a data structure optimized to count frequencies against data that is stored in a database table-like format. for example, the data comes in a (comma) delimited format below. col1, col2, col3 x, a, green x, b, blue ... y, c, green now i simply want to count the frequency of col1=x or col1=x and col2=green. i have been storing the data in a database table, but in my profiling and from empirical observation, database connection is the bottle-neck. i have tried using in-memory database solutions too, and that works quite well; the only problem is memory requirements and quirky init/destroy calls. also, i work mainly with java, but have experience with .net, and was wondering if there was any api to work with "tabular" data in a linq way using java. any help is appreciated.

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• Data structure for an ordered set with many defined subsets; retrieve subsets in same order

  - by Aaron

  I'm looking for an efficient way of storing an ordered list/set of items where: The order of items in the master set changes rapidly (subsets maintain the master set's order) Many subsets can be defined and retrieved The number of members in the master set grow rapidly Members are added to and removed from subsets frequently Must allow for somewhat efficient merging of any number of subsets Performance would ideally be biased toward retrieval of the first N items of any subset (or merged subset), and storage would be in-memory (and maybe eventually persistent on disk)

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• Chess board position numbers in 6-rooted-binary tree?

  - by HH

  The maximum number of adjacent vertices is 6 that corresponds to the number of roots. By the term root, I mean the number of children for each node. If adjacent square is empty, fill it with Z-node. So every square will have 6 nodes. How can you formulate it with binary tree? Is the structure just 6-rooted-binary tree? What is the structure called if nodes change their positions? Suppose partially ordered list where its units store a large randomly expanding board. I want a self-adjusting data structure, where it is easy to calculate distances between nodes. What is its name?

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• How to optimize this Python code?

  - by RandomVector

  def maxVote(nLabels): count = {} maxList = [] maxCount = 0 for nLabel in nLabels: if nLabel in count: count[nLabel] += 1 else: count[nLabel] = 1 #Check if the count is max if count[nLabel] > maxCount: maxCount = count[nLabel] maxList = [nLabel,] elif count[nLabel]==maxCount: maxList.append(nLabel) return random.choice(maxList) nLabels contains a list of integers. The above function returns the integer with highest frequency, if more than one have same frequency then a randomly selected integer from them is returned. E.g. maxVote([1,3,4,5,5,5,3,12,11]) is 5

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• JavaScript - question regarding data structure

  - by orokusaki

  I'm trying to calculate somebody's bowel health based on a points system. I can edit the data structure, or logic in any way. I'm just trying to write a function and data structure to handle this ability. Pseudo calculator function: // Bowel health calculator var points = 0; If age is from 30 and 34: points += 1 If age is from 35 and 40: points += 2 If daily BMs is from 1 and 3: points -= 1 If daily BMs is from 4 and 6: points -= 2 return points; Pseudo data structure: var points_map = { age: { '30-34': 1, '35-40': 2 }, dbm: { '1-3': -1, '4-6': -2 } }; I have a full spreadsheet of data like this, and I am trying to write a DRY version of code and a DRY version of this data (ie, probably not a string for the '30-34', etc) in order to handle this sort of thing without a humongous number of switch statements.

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• How do I remove the leaves of a binary tree?

  - by flopex

  I'm trying to remove all of the leaves. I know that leaves have no children, this is what I have so far. public void removeLeaves(BinaryTree n){ if (n.left == null && n.right == null){ n = null; } if (n.left != null) removeLeaves(n.left); if (n.right != null) removeLeaves(n.right); }

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• Better data-structure design

  - by Tempname

  Currently in my application I have a single table that is giving me a bit of trouble. The issue at hand is I have a value object that is mapped to this table. When the data is returned to me as an array of value objects, I have to then loop through this array and begin my recursion by matching the ParentID to parent ObjectID's. The column ParentID is either null (acts a parent) or it holds the value of an ObjectID. I know there has to be a better way to create this data structure so that I do not have to do recursive loops to match ParentID's with their ObjectID's. Any help with this is greatly appreciated. Here is the table in describe form: +----------------+------------------+------+-----+---------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------+------------------+------+-----+---------------------+-----------------------------+ | ObjectID | int(11) unsigned | NO | PRI | NULL | auto_increment | | ObjectHeight | decimal(6,2) | NO | | NULL | | | ObjectWidth | decimal(6,2) | NO | | NULL | | | ObjectX | decimal(6,2) | NO | | NULL | | | ObjectY | decimal(6,2) | NO | | NULL | | | ObjectLabel | varchar(255) | NO | | NULL | | | TemplateID | int(11) unsigned | NO | MUL | NULL | | | ObjectTypeID | int(11) unsigned | NO | MUL | NULL | | | ParentID | int(11) unsigned | YES | MUL | NULL | | | CreationDate | datetime | YES | | 0000-00-00 00:00:00 | | | LastModifyDate | timestamp | YES | | NULL | on update CURRENT_TIMESTAMP | +----------------+------------------+------+-----+---------------------+-----------------------------+e

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• Binary tree to BST

  - by dsiap

  How wil you convert Binary Tree to Binary Search Tree with O(n) extra space ?

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• When does it make sense to use a map?

  - by kiwicptn

  I am trying to round up cases when it makes sense to use a map (set of key-value entries). So far I have two categories (see below). Assuming more exist, what are they? Please limit each answer to one unique category and put up an example. Property values (like a bean) age -> 30 sex -> male loc -> calgary Presence, with O(1) performance peter -> 1 john -> 1 paul -> 1

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• C - How to implement Set data structure?

  - by psihodelia

  Is there any tricky way to implement a set data structure (a collection of unique values) in C? All elements in a set will be of the same type and there is a huge RAM memory. As I know, for integers it can be done really fast'N'easy using value-indexed arrays. But I'd like to have a very general Set data type. And it would be nice if a set could include itself.

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• implementation of a queue using a circular array

  - by matin1234

  Hi I have found these algorithms in the internet but I can not understand that why in the enqueue method we compare size with N-1??? please help me thanks!! Algorithm size(): return (N-f+r)mod N Algorithm enqueue(e): if size()=N-1 then throw a FullQueueException Q[r]<---e r<----(r+1)mod N

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• Python method to remove iterability

  - by Debilski

  Suppose I have a function which can either take an iterable/iterator or a non-iterable as an argument. Iterability is checked with try: iter(arg). Depending whether the input is an iterable or not, the outcome of the method will be different. Not when I want to pass a non-iterable as iterable input, it is easy to do: I’ll just wrap it with a tuple. What do I do when I want to pass an iterable (a string for example) but want the function to take it as if it’s non-iterable? E.g. make that iter(str) fails.

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• basic json > struct question

  - by danwoods

  I'm working with twitter's api, trying to get the json data from http://search.twitter.com/trends/current.json which looks like: {"as_of":1268069036,"trends":{"2010-03-08 17:23:56":[{"name":"Happy Women's Day","query":"\"Happy Women's Day\" OR \"Women's Day\""},{"name":"#MusicMonday","query":"#MusicMonday"},{"name":"#MM","query":"#MM"},{"name":"Oscars","query":"Oscars OR #oscars"},{"name":"#nooffense","query":"#nooffense"},{"name":"Hurt Locker","query":"\"Hurt Locker\""},{"name":"Justin Bieber","query":"\"Justin Bieber\""},{"name":"Cmon","query":"Cmon"},{"name":"My World 2","query":"\"My World 2\""},{"name":"Sandra Bullock","query":"\"Sandra Bullock\""}]}} My structs look like: type trend struct { name string query string } type trends struct { id string arr_of_trends []trend } type Trending struct { as_of string trends_obj trends } and then I parse the JSON into a variable of type Trending. I'm very new to JSON so my main concern is making sure I've have the data structure correctly setup to hold the returned json data. I'm writing this in 'Go' for a project for school. (This is not part of a particular assignment, just something I'm demo-ing for a presentation on the language)

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• Good ways to map a 2D side shooter (somewhat like liero, or soldat)

  - by Blaze

  I'm wondering what way would be best to render a 2D map for a shooter (these will be static maps) similar to Soldat. Multiple options I've considered are a tile based map (stored in txt files), or just creating different classes for the different terrains I plan to use and creating a data structure to read/store them in a file. (I want to also be able to include things like jumping/running on walls, sliding down walls/slopes ect) I feel like there must be a better way than either of these, but haven't been able to find definitive information :/ Thanks :)

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