backtracking

I'm doing a very simple exercise in Prolog and there's something I don't understand in the trace. The program is a "greater than" ( > ) on integers represented as successors: greater_than(succ(_), 0). greater_than(succ(A), succ(B)) :- greater_than(A, B). My problem: I don't understand why the request greater_than(succ(succ(succ(0))),succ(0)) generates a redo in the following trace: [trace] ?- greater_than(succ(succ(succ(0))),succ(0)). Call: (6) greater_than(succ(succ(succ(0))), succ(0)) ? creep Call: (7) greater_than(succ(succ(0)), 0) ? creep Exit: (7) greater_than(succ(succ(0)), 0) ? creep

I created a Sudoku Backtracking solver and it works just fine, but now i want to give out an error if the sudoku cant be solved because it isnt valid for example if this sudoku is given: http://img5.imageshack.us/img5/2241/sudokugq.jpg what can i do to make my solving method give out an error if it isnt solveable? I always end up with Zeros or stuck in a loop. public void solve( int row, int col ) throws Exception { // Throw an exception to stop the process if the puzzle is solved if( row > 8 ){ //Gelöst } // If the cell is not empty, continue with the next cell if( sudo[row][col] != 0 ){ next

I have this homework assignment to make a recursive method to crack a password of a given length, n (unlimited and unknown!) made of small English letters, a-z ONLY. Here's the class "Password" that creates a random password: import java.util.Random; public class Password { private String _password = ""; public Password(int length) { Random generator = new Random(); for (int i = 0; i < length; ++i) { this._password = this._password + (char) (generator.nextInt(26) + 97); } } public boolean isPassword(String st) { return st.equals(this._password); } public String getPassword() { return this.

I'm trying to write code for the Knight's Tour : A knight's tour is a sequence of moves of a knight on a chessboard such that the knight visits every square exactly once. I've been trying to alter someone else's code, but the backtracking seems to not work properly - it never finds the solution. It works perfectly fine when the knight starts at 0, 0 but if it starts at any other spot on the 2D grid, the program goes on forever. Where is the bug in this code? #include <iostream> #include <ctime> using namespace std; const int N = 8; int map[N][N]; /* A utility function to check if i,j are valid

I was reading the code below on Geeksforgeeks, but I just can't wrap my head around how it works! If anyone can explain it pictorially. That'd be great! this is the code: static void swap(char a[], int l, int r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } static void permute(char a[], int l, int r) { if (l == r) System.out.println(getString(a)); else { for (int i = l; i <= r; i++) { swap(a, l, i); permute(a, l + 1, r); swap(a, l, i); // backtrack } } } I don't see where you're confused: you provided a picture that explains it quite clearly ... to me. :-) Termination condition (bottom row

As a generically brewed example for the purpose of this question, my intent is to match some number of a 's, then an equal number of b 's, plus one more b . Examine the two patterns exhibited in this snippet ( also on ideone.com ): var r1 = new Regex(@"(?xn) (?<A> a)+ (?<B-A> b)+ (?(A)(?!)) b "); var r2 = new Regex(@"(?xn) (?<A> a)+ (?<B-A> b)+? (?(A)(?!)) b "); Console.WriteLine(r1.Match("aaabbb")); // aaabbb Console.WriteLine(r2.Match("aaabbb")); // aabbb Note that there is a difference in the matches of the two patterns. r1 , which uses a greedy repetition on the balancing group construct,

Now I'm working with the recursive backtracking,my assignment is to find the longest path in the maze,the mass is presented as the field covered with the coordinates,and the coordinates of the walls are sore in the file. I have made a parser to parse the input file and build the walls,but I have also stored this coordinates in the array of an object type Coordinate,to check whether it is possible to move the next piece of the "snake" on the next field,then I have created this method,now I have understood that I will need a method to remove the last coordinate from the array when I will use

i'm trying to write a Sudoku solver which will return only the first possible solution. i managed to print all possible solutions with void methods but i can't stop on the first find. i know the preferred way is to switch to boolean methods and return true up the tree - but i can't find the right way to write it. any way i tried always give compilation errors ( method must return boolean ). public boolean recursiveSolve(int line, int column) { if(line == N) // N is the board size (9) return true; // if Cell is not empty - continue if(board1.getCell(line, column) != 0) { return nextCell(line,