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  • Theory of computation - Using the pumping lemma for CFLs

    - by Tony
    I'm reviewing my notes for my course on theory of computation and I'm having trouble understanding how to complete a certain proof. Here is the question: A = {0^n 1^m 0^n | n>=1, m>=1} Prove that A is not regular. It's pretty obvious that the pumping lemma has to be used for this. So, we have |vy| = 1 |vxy| <= p (p being the pumping length, = 1) uv^ixy^iz exists in A for all i = 0 Trying to think of the correct string to choose seems a bit iffy for this. I was thinking 0^p 1^q 0^p, but I don't know if I can obscurely make a q, and since there is no bound on u, this could make things unruly.. So, how would one go about this?

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  • Dynamic programming: Largest diamond(rhombus) block

    - by Darksody
    I have a small program to do in Java. I have a 2D array filled with 0 and 1, and I must find the largest rhombus (as in square rotated by 90 degrees) and their numbers. Example: 0 1 0 0 0 1 1 0 1 1 1 0 1 0 1 1 1 1 0 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 Result: 1 1 1 1 1 1 1 1 1 1 1 1 1 The problem is similar to this SO question. If you have any idea, post it here.

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  • Problem on a Floyd-Warshall implementation using c++

    - by Henrique
    I've got a assignment for my college, already implemented Dijkstra and Bellman-Ford sucessfully, but i'm on trouble on this one. Everything looks fine, but it's not giving me the correct answer. Here's the code: void FloydWarshall() { //Also assume that n is the number of vertices and edgeCost(i,i) = 0 int path[500][500]; /* A 2-dimensional matrix. At each step in the algorithm, path[i][j] is the shortest path from i to j using intermediate vertices (1..k-1). Each path[i][j] is initialized to edgeCost(i,j) or infinity if there is no edge between i and j. */ for(int i = 0 ; i <= nvertices ; i++) for(int j = 0 ; j <= nvertices ; j++) path[i][j] = INFINITY; for(int j = 0 ; j < narestas ; j++) //narestas = number of edges { path[arestas[j]->v1][arestas[j]->v2] = arestas[j]->peso; //peso = weight of the edge (aresta = edge) path[arestas[j]->v2][arestas[j]->v1] = arestas[j]->peso; } for(int i = 0 ; i <= nvertices ; i++) //path(i, i) = 0 path[i][i] = 0; //test print, it's working fine //printf("\n\n\nResultado FloydWarshall:\n"); //for(int i = 1 ; i <= nvertices ; i++) // printf("distancia ao vertice %d: %d\n", i, path[1][i]); //heres the problem, it messes up, and even a edge who costs 4, and the minimum is 4, it prints 2. //for k = 1 to n for(int k = 1 ; k <= nvertices ; k++) //for i = 1 to n for(int i = 1 ; i <= nvertices ; i++) //for j := 1 to n for(int j = 1 ; j <= nvertices ; j++) if(path[i][j] > path[i][k] + path[k][j]) path[i][j] = path[i][k] + path[k][j]; printf("\n\n\nResultado FloydWarshall:\n"); for(int i = 1 ; i <= nvertices ; i++) printf("distancia ao vertice %d: %d\n", i, path[1][i]); } im using this graph example i've made: 6 7 1 2 4 1 5 1 2 3 1 2 5 2 5 6 3 6 4 6 3 4 2 means we have 6 vertices (1 to 6), and 7 edges (1,2) with weight 4... etc.. If anyone need more info, i'm up to giving it, just tired of looking at this code and not finding an error.

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  • Using recursion to to trim a binary tree based on a given min and max value

    - by Justin
    As the title says, I have to trim a binary tree based on a given min and max value. Each node stores a value, and a left/right node. I may define private helper methods to solve this problem, but otherwise I may not call any other methods of the class nor create any data structures such as arrays, lists, etc. An example would look like this: overallRoot _____[50]____________________ / \ __________[38] _______________[90] / \ / _[14] [42] [54]_____ / \ \ [8] [20] [72] \ / \ [26] [61] [83] trim(52, 65); should return: overallRoot [54] \ [61] My attempted solution has three methods: public void trim(int min, int max) { rootFinder(overallRoot, min, max); } First recursive method finds the new root perfectly. private void rootFinder(IntTreeNode node, int min, int max) { if (node == null) return; if (overallRoot.data < min) { node = overallRoot = node.right; rootFinder(node, min, max); } else if (overallRoot.data > max) { node = overallRoot = node.left; rootFinder(node, min, max); } else cutter(overallRoot, min, max); } This second method should eliminate any further nodes not within the min/max, but it doesn't work as I would hope. private void cutter(IntTreeNode node, int min, int max) { if (node == null) return; if (node.data <= min) { node.left = null; } if (node.data >= max) { node.right = null; } if (node.data < min) { node = node.right; } if (node.data > max) { node = node.left; } cutter(node.left, min, max); cutter(node.right, min, max); } This returns: overallRoot [54]_____ \ [72] / [61] Any help is appreciated. Feel free to ask for further explanation as needed.

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  • Finding specific words in a file (Python language)

    - by Caroline Yi
    I have to write a program in python where the user is given a menu with four different "word games". There is a file called dictionary.txt and one of the games requires the user to input a) the number of letters in a word and b) a letter to exclude from the words being searched in the dictionary (dictionary.txt has the whole dictionary). Then the program prints the words that follow the user's requirements. My question is how on earth do I open the file and search for words with a certain length in that file. I only have a basic code which only asks the user for inputs. I'm am very new at this please help :( this is what I have up to the first option. The others are fine and I know how to break the loop but this specific one is really giving me trouble. I have tried everything and I just keep getting errors. Honestly, I only took this class because someone said it would be fun. It is, but recently I've really been falling behind and I have no idea what to do now. This is an intro level course so please be nice I've never done this before until now :( print print "Choose Which Game You Want to Play" print "a) Find words with only one vowel and excluding a specific letter." print "b) Find words containing all but one of a set of letters." print "c) Find words containing a specific character string." print "d) Find words containing state abbreviations." print "e) Find US state capitals that start with months." print "q) Quit." print choice = raw_input("Enter a choice: ") choice = choice.lower() print choice while choice != "q": if choice == "a": #wordlen = word length user is looking for.s wordlen = raw_input("Please enter the word length you are looking for: ") wordlen = int(wordlen) print wordlen #letterex = letter user wishes to exclude. letterex = raw_input("Please enter the letter you'd like to exclude: ") letterex = letterex.lower() print letterex

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  • python programme.

    - by siva
    hi, i am siva this is frist time taken the python programming language i have a small problem please help me the question is **Write two functions, called countSubStringMatch and countSubStringMatchRecursive that take two arguments, a key string and a target string. These functions iteratively and recursively count the number of instances of the key in the target string. You should complete definitions for def countSubStringMatch(target,key): and def countSubStringMatchRecursive (target, key): **

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  • Write a program that allows the user to enter a string and then prints the letters of the String sep

    - by WM
    The output is always a String, for example H,E,L,L,O,. How could I limit the commas? I want the commas only between letters, for example H,E,L,L,O. import java.util.Scanner; import java.lang.String; public class forLoop { public static void main(String[] args) { Scanner Scan = new Scanner(System.in); System.out.print("Enter a string: "); String Str1 = Scan.next(); String newString=""; String Str2 =""; for (int i=0; i < Str1.length(); i++) { newString = Str1.charAt(i) + ","; Str2 = Str2 + newString; } System.out.print(Str2); } }

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  • java interfaces

    - by Codenotguru
    write an interface with one method,two classes that implement the interface, and a main method with an array holding an instance from both classes.Using this array variable call the method in a foreach loop.This is a interview question in java anybody?

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  • Exception Class: When to Derive from it, In C# (.Net)?

    - by IbrarMumtaz
    I am continuing with my exam revision. I have come across the usage of the Base Exception class and I have seen it on exam papers also. My question is when do you derive from the Base Exception class? I am of the impression if you want a custom class to throw an exception with more meaningful information, then you can create a custom exception class that contains the exact data that is representative of how your custom class is used and what scenario it is designed to be used for? Why can't my custom exception class derive from 'ApplicationException' or 'SecurityException' or the base 'Exception' class? I am of the impression that I should derive from the base Exception class and not the previous two. My question second is, when would you derive from the other two??? Are there any clear-cut distinctions as to when you would derive from either one of these three? Assuming there are no others I have I have missed out? Thanks, Ibrar

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  • Returning the element number of the longest string in an array

    - by JohnRoberts
    I'm trying to get the longestS method to take the user-inputted array of strings, then return the element number of the longest string in that array. I got it to the point where I was able to return the number of chars in the longest string, but I don't believe that will work for what I need. My problem is that I keep getting incompatible type errors when trying to figure this out. I don't understand the whole data type thing with strings yet. It's confusing me how I go about return a number of the array yet the array is of strings. The main method is fine, I got stuck on the ???? part. { public static void main(String [] args) { Scanner inp = new Scanner( System.in ); String [] responseArr= new String[4]; for (int i=0; i<4; i++) { System.out.println("Enter string "+(i+1)); responseArr[i] = inp.nextLine(); } int highest=longestS(responseArr); } public static int longestS(String[] values) { int largest=0 for( int i = 1; i < values.length; i++ ) { if ( ????? ) } return largest; } }

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  • Problem in finalizing the link list in C#

    - by Yasin
    My code was almost finished that a maddening bug came up! when i nullify the last node to finalize the link list , it actually dumps all the links and make the first node link Null ! when i trace it , its working totally fine creating the list in the loop but after the loop is done that happens and it destroys the rest of the link by doing so, and i don't understand why something so obvious is becoming problematic! (last line) struct poly { public int coef; public int pow; public poly* link;} ; poly* start ; poly* start2; poly* p; poly* second; poly* result; poly* ptr; poly* start3; poly* q; poly* q2; private void button1_Click(object sender, EventArgs e) { string holder = ""; IntPtr newP = Marshal.AllocHGlobal(sizeof(poly)); q = (poly*)newP.ToPointer(); start = q; int i = 0; while (this.textBox1.Text[i] != ',') { holder += this.textBox1.Text[i]; i++; } q->coef = int.Parse(holder); i++; holder = ""; while (this.textBox1.Text[i] != ';') { holder += this.textBox1.Text[i]; i++; } q->pow = int.Parse(holder); holder = ""; p = start; //creation of the first node finished! i++; for (; i < this.textBox1.Text.Length; i++) { newP = Marshal.AllocHGlobal(sizeof(poly)); poly* test = (poly*)newP.ToPointer(); while (this.textBox1.Text[i] != ',') { holder += this.textBox1.Text[i]; i++; } test->coef = int.Parse(holder); holder = ""; i++; while (this.textBox1.Text[i] != ';' && i < this.textBox1.Text.Length - 1) { holder += this.textBox1.Text[i]; if (i < this.textBox1.Text.Length - 1) i++; } test->pow = int.Parse(holder); holder = ""; p->link = test; //the addresses are correct and the list is complete } p->link = null; //only the first node exists now with a null link! }

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  • Unknown error in Producer/Consumer program, believe it to be an infinite loop.

    - by ray2k
    Hello, I am writing a program that is solving the producer/consumer problem, specifically the bounded-buffer version(i believe they mean the same thing). The producer will be generating x number of random numbers, where x is a command line parameter to my program. At the current moment, I believe my program is entering an infinite loop, but I'm not sure why it is occurring. I believe I am executing the semaphores correctly. You compile it like this: gcc -o prodcon prodcon.cpp -lpthread -lrt Then to run, ./prodcon 100(the number of randum nums to produce) This is my code. typedef int buffer_item; #include <stdlib.h> #include <stdio.h> #include <pthread.h> #include <semaphore.h> #include <unistd.h> #define BUFF_SIZE 10 #define RAND_DIVISOR 100000000 #define TRUE 1 //two threads void *Producer(void *param); void *Consumer(void *param); int insert_item(buffer_item item); int remove_item(buffer_item *item); int returnRandom(); //the global semaphores sem_t empty, full, mutex; //the buffer buffer_item buf[BUFF_SIZE]; //buffer counter int counter; //number of random numbers to produce int numRand; int main(int argc, char** argv) { /* thread ids and attributes */ pthread_t pid, cid; pthread_attr_t attr; pthread_attr_init(&attr); pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM); numRand = atoi(argv[1]); sem_init(&empty,0,BUFF_SIZE); sem_init(&full,0,0); sem_init(&mutex,0,0); printf("main started\n"); pthread_create(&pid, &attr, Producer, NULL); pthread_create(&cid, &attr, Consumer, NULL); printf("main gets here"); pthread_join(pid, NULL); pthread_join(cid, NULL); printf("main done\n"); return 0; } //generates a randum number between 1 and 100 int returnRandom() { int num; srand(time(NULL)); num = rand() % 100 + 1; return num; } //begin producing items void *Producer(void *param) { buffer_item item; int i; for(i = 0; i < numRand; i++) { //sleep for a random period of time int rNum = rand() / RAND_DIVISOR; sleep(rNum); //generate a random number item = returnRandom(); //acquire the empty lock sem_wait(&empty); //acquire the mutex lock sem_wait(&mutex); if(insert_item(item)) { fprintf(stderr, " Producer report error condition\n"); } else { printf("producer produced %d\n", item); } /* release the mutex lock */ sem_post(&mutex); /* signal full */ sem_post(&full); } return NULL; } /* Consumer Thread */ void *Consumer(void *param) { buffer_item item; int i; for(i = 0; i < numRand; i++) { /* sleep for a random period of time */ int rNum = rand() / RAND_DIVISOR; sleep(rNum); /* aquire the full lock */ sem_wait(&full); /* aquire the mutex lock */ sem_wait(&mutex); if(remove_item(&item)) { fprintf(stderr, "Consumer report error condition\n"); } else { printf("consumer consumed %d\n", item); } /* release the mutex lock */ sem_post(&mutex); /* signal empty */ sem_post(&empty); } return NULL; } /* Add an item to the buffer */ int insert_item(buffer_item item) { /* When the buffer is not full add the item and increment the counter*/ if(counter < BUFF_SIZE) { buf[counter] = item; counter++; return 0; } else { /* Error the buffer is full */ return -1; } } /* Remove an item from the buffer */ int remove_item(buffer_item *item) { /* When the buffer is not empty remove the item and decrement the counter */ if(counter > 0) { *item = buf[(counter-1)]; counter--; return 0; } else { /* Error buffer empty */ return -1; } }

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  • Available message types in JMS?

    - by Caylem
    This is based on a past exam question. The question is asking to describe the four types of message available using JMS. The problem is it says the four, not just four. So it assumes their is only four, no more no less. However according to this site their seems to be five; streams maps text objects bytes *Another book states that XML is another potential type in future versions of JMS. Is XML already available? Am I missing something or is the question just wrong? Thanks.

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  • Candidate Elimination Question---Please help!

    - by leon
    Hi , I am doing a question on Candidate Elimination Algorithm. I am a little confused with the general boundary G. Here is an example, I got G and S to the fourth case, but I am not sure with the last case. Sunny,Warm,Normal,Strong,Warm,Same,EnjoySport=yes Sunny,Warm,High,Strong,Warm,Same,EnjoySport=yes Rainy,Cold,High,Strong,Warm,Change,EnjoySport=no Sunny,Warm,High,Strong,Cool,Change,EnjoySport=yes Sunny,Warm,Normal,Weak,Warm,Same,EnjoySport=no What I have here is : S 0 :{0,0,0,0,0,0} S 1 :{Sunny,Warm,Normal,Strong,Warm,Same} S 2 , S 3 : {Sunny,Warm,?,Strong,Warm,Same} S 4 :{Sunny,Warm,?,Strong,?,?} G 4 :{Sunny,?,?,?,?,?,?,Warm,?,?,?,?} G 3 :{Sunny,?,?,?,?,?,?,Warm,?,?,?,?,?,?,?,?,?,Same} G 0 , G 1 , G 2 : {?,?,?,?,?,?} What would be the result of G5? Is it G5 empty? {}? or {???Strong??) ? Thanks

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  • Help with a sort method

    - by Capsud
    Hi there, If i have an array of strings for example Static final String[] TEST = new String[] { "g","a","b","t","e" }; How would i go about sorting this in alphabetical order please?

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  • clearing cin input? cin.ignore not a good way?

    - by igor
    What's a better way to clear cin input? I thought cin.clear and cin.ignore was a good way...? code: void clearInput() { cin.clear(); cin.ignore(1000,'\n'); //cin.ignore( std::numeric_limits<streamsize>::max(), '\n' ); } My teacher gave me this reply... this is basically saying that your clearInput doesn't work FYI: ignore is NEVER a good idea as a way of getting rid of all that remains on a line and your failing this test is exactly the reason why now go clear it the correct way

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  • using compareTo in Binary Search Tree program

    - by Scott Rogener
    I've been working on this program for a few days now and I've implemented a few of the primary methods in my BinarySearchTree class such as insert and delete. Insert seemed to be working fine, but once I try to delete I kept getting errors. So after playing around with the code I wanted to test my compareTo methods. I created two new nodes and tried to compare them and I get this error: Exception in thread "main" java.lang.ClassCastException: TreeNode cannot be cast to java.lang.Integer at java.lang.Integer.compareTo(Unknown Source) at TreeNode.compareTo(TreeNode.java:16) at BinarySearchTree.myComparision(BinarySearchTree.java:177) at main.main(main.java:14) Here is my class for creating the nodes: public class TreeNode<T> implements Comparable { protected TreeNode<T> left, right; protected Object element; public TreeNode(Object obj) { element=obj; left=null; right=null; } public int compareTo(Object node) { return ((Comparable) this.element).compareTo(node); } } Am I doing the compareTo method all wrong? I would like to create trees that can handle integers and strings (seperatly of course)

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  • String operations

    - by NEO
    I am trying to find the most repeated word in a string. My code is as follows: public class Word { private String toWord; private int Count; public Word(int count, String word){ toWord = word; Count = count; } public static void main(String args[]){ String str="my name is neo and my other name is also neo because I am neo"; String []str1=str.split(" "); Word w1=new Word(0,str1[0]); LinkedList<Word> list = new LinkedList<Word>(); list.add(w1); ListIterator itr = list.listIterator(); for(int i=1;i<str1.length;i++){ while(itr.hasNext()){ if(str1[i].equalsTO(????)); else list.add(new Word(0,str1[i])); } How do I compare the string from string array str1 to the string stored in the linked list and then how do i increase the respective count. I will then print the string with the highest count, I dont know how to do that either.

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