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matthewsamuel95matthewsamuel95
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Merge pull request #576 from anirudherabelly/master
added other language implementation of backtracking algorithms.
2 parents f31b10f + ce2530e commit a809eb4

5 files changed

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‎BackTracking/KnightsTour/KnightsTour.cs‎

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

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

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

‎BackTracking/RatInAMaze/RatInMaze.cs‎

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