Merge pull request matthewsamuel95#576 from anirudherabelly/master

added other language implementation of backtracking algorithms.

BackTracking/KnightsTour/KnightsTour.cs

@@ -0,0 +1,70 @@
+/*
+move Knight in a chess board such that it covers all the cells atleast once.
+*/
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GFG
+{
+    class Program
+    {
+        static void Main(String[] args)
+        {
+            int[,] board = new int[8,8];
+            Intialize(board);
+            int[] rowx = { 2, 1, -1, -2, -2, -1, 1, 2 };
+            int[] coly = { 1, 2, 2, 1, -1, -2, -2, -1 };
+            if (KnightsTour(board, 0, 0, 1,rowx,coly)) Display(board);
+            else Console.WriteLine("Solution does not exist");      
+        }
+        private static void Intialize(int[,] board)
+        {
+            for (int i = 0; i < 8; i++)
+            {
+                for (int j = 0; j < 8; j++)
+                {
+                    board[i, j]=-1;
+                }
+            }
+            board[0, 0] = 0;
+        }
+        private static void Display(int[,] board)
+        {
+            for(int i = 0; i < 8; i++)
+            {
+                for(int j = 0; j < 8; j++)
+                {
+                    Console.Write(board[i,j]+" ");
+                }
+                Console.WriteLine();
+            }
+        }
+        private static bool KnightsTour(int[,] board, int row, int col,int move,int[] rowx,int[] coly)
+        {
+            if (move == 64) return true;
+            int nextx, nexty;
+            for(int k = 0; k < 8; k++)
+            {
+                nextx = row+rowx[k];
+                nexty = col+coly[k];
+                if (IsSafe(board, nextx, nexty))
+                {
+                    board[nextx, nexty] = move;
+                    if(KnightsTour(board,nextx,nexty,move+1,rowx,coly))return true;
+                    board[nextx, nexty] = -1;
+                }
+            }
+            return false;
+        }
+
+        private static bool IsSafe(int[,] board, int row, int col)
+        {
+            if (row >= 0 && row < 8 && col >= 0 && col < 8 && board[row, col] == -1) return true;
+            return false;
+        }
+    }
+}
+

BackTracking/NQueens/NQueens.cs

@@ -0,0 +1,106 @@
+/*
+The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.
+Given an integer n, print all distinct solutions to the n-queens puzzle.
+Each solution contains distinct board configurations of the n-queens’ placement,
+where the solutions are a permutation of [1,2,3..n] in increasing order,
+here the number in the ith place denotes that the ith-column queen is placed in the row with that number.
+For eg below figure represents a chessboard [3 1 4 2].
+[0,0,Q,0]
+[Q,0,0,0]
+[0,0,0,Q]
+[0,Q,0,0]
+Input:
+The first line of input contains an integer T denoting the no of test cases.
+Then T test cases follow. Each test case contains an integer n denoting the size of the chessboard.
+
+Output:
+For each test case, output your solutions on one line where each solution is enclosed in square brackets 
+'[', ']' separated by a space . The solutions are permutations of {1, 2, 3 …, n} in increasing order where 
+the number in the ith place denotes the ith-column queen is placed in the row with that number, 
+if no solution exists print -1.
+
+Constraints:
+1<=T<=10
+1<=n<=10
+
+Example:
+Input
+2
+1
+4
+Output:
+[1 ]
+[2 4 1 3 ] [3 1 4 2 ]
+*/
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GFG
+{
+    class Program
+    {
+        static bool resultFound=false; 
+        static void Main(String[] args)
+        {
+            int t = Int32.Parse(Console.ReadLine());
+            for(int i = 0; i < t; i++)
+            {
+                int n= Int32.Parse(Console.ReadLine());
+                int[,] board = new int[n,n];
+                Nqueen(board,0,n);
+                if (!resultFound) Console.Write(-1);
+                Console.WriteLine();
+            }   
+        }
+        private static void Display(int[,] board, int n)
+        {
+            Console.Write("[");
+            for(int i = 0; i < n; i++)
+            {
+                for(int j = 0; j < n; j++)
+                {
+                    if (board[j, i] == 1)Console.Write(j + 1+" ");
+                }
+            }
+            Console.Write("]");
+        }
+        private static void Nqueen(int[,] board, int col, int n)
+        {
+            if (col >= n)
+            {
+                resultFound = true;
+                Display(board,n);
+                return;
+            }
+            for(int i = 0; i < n; i++)
+            {
+                if (IsSafe(board, i, col, n))
+                {
+                    board[i, col] = 1;
+                    Nqueen(board, col + 1, n);
+                    board[i, col] = 0;
+                }
+            }
+        }
+        private static bool IsSafe(int[,] board, int row, int col, int n)
+        {
+            for(int i = 0; i < col; i++)
+            {
+                if (board[row, i] == 1) return false;
+            }
+            for(int i=row,j=col;i>=0 && j >=0; i--, j--)
+            {
+                if (board[i, j] == 1) return false;
+            }
+            for(int i=row,j=col;i<n && j >= 0; i++, j--)
+            {
+                if (board[i, j] == 1) return false;
+            }
+            return true;
+        }
+    }
+}
+

BackTracking/Permutation/GeneratePermutations.cs

@@ -0,0 +1,43 @@
+/*
+sb=abc
+
+output:
+abc
+acb
+bac
+bca
+cba
+cab
+*/
+using System;
+using System.Text;
+
+namespace Hackerearth
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            StringBuilder sb = new StringBuilder(Console.ReadLine());
+            int n = sb.Length;
+            GeneratePermutations(sb,0,n-1);
+        }
+        private static void GeneratePermutations(StringBuilder sb, int l,int r)
+        {
+            if (l == r) Console.WriteLine(sb);
+            for (int i = l; i <= r; i++)
+            {
+                swap(sb, l,i);
+                GeneratePermutations(sb,l+1,r);
+                swap(sb,l,i);
+            }
+
+        }
+        private static void swap(StringBuilder sb, int i, int j)
+        {
+            char temp = sb[i];
+            sb[i] = sb[j];
+            sb[j] = temp;
+        }
+    }
+}

BackTracking/RatInAMaze/RatInMaze.cs

@@ -0,0 +1,76 @@
+/*
+Consider a rat placed at (0, 0) in a square matrix m[][] of order n and has to reach the destination at (n-1, n-1).
+Your task is to complete the function which returns a sorted array of strings denoting all the possible directions 
+which the rat can take to reach the destination at (n-1, n-1). The directions in which the rat can move are 'U'(up), 
+'D'(down), 'L' (left), 'R' (right).
+
+For example
+1 0 0 0
+1 1 0 1
+1 1 0 0
+0 1 1 1
+
+For the above matrix the rat can reach the destination at (3, 3) from (0, 0) by two paths ie DRDDRR and DDRDRR 
+when printed in sorted order we get DDRDRR DRDDRR.
+*/
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GFG
+{
+    class Program
+    {
+        static void Main(String[] args)
+        {
+            int t = Int32.Parse(Console.ReadLine());
+            for (int i = 0; i < t; i++)
+            {
+                int n = Int32.Parse(Console.ReadLine());
+                int[] rc = Array.ConvertAll(Console.ReadLine().Split(' '),Int32.Parse);
+                int[,] grid = new int[n,n];
+                bool[,] visited = new bool[n,n];
+                for(int j = 0; j < n; j++)
+                {
+                    for(int k = 0; k < n; k++)
+                    {
+                        grid[j, k] = rc[(j*n)+k];
+                    }
+                }
+                if (grid[0, 0] == 1) RatPuzzle(grid,visited, n, 0, 0, "");
+                else Console.WriteLine("not possible");
+            }
+        }
+        private static void RatPuzzle(int[,] grid,bool[,] visited, int n,int row,int col,string s)
+        {
+            visited[row, col] = true;
+
+            if (row >= n || col >= n || row <0 || col<0) return ;
+            if (row == (n - 1) && col == (n - 1))
+            {
+                Console.WriteLine(s+" ");
+            }
+
+            if ((row+1)<n && grid[row + 1, col] == 1 && !visited[row+1,col])
+            {
+                RatPuzzle(grid, visited, n, row + 1, col, s+"D");
+            }
+            if ((col - 1) >= 0 && grid[row, col - 1] == 1 && !visited[row, col - 1])
+            {
+                RatPuzzle(grid, visited, n, row, col - 1, s+"L");
+            }
+            if ((col + 1) < n && grid[row, col + 1] == 1 && !visited[row,col+1])
+            {
+                RatPuzzle(grid, visited, n, row, col + 1, s+"R");
+            }
+            if ((row-1)>=0 && grid[row-1, col] == 1 && !visited[row-1,col])
+            {
+                RatPuzzle(grid,visited, n, row-1, col, s+"U");
+            }
+            visited[row, col] = false;
+        }
+    }
+}
+