N_Queen.cpp

#include<iostream>
using namespace std;
#define N 4
void printBoard(int board[N][N]) {
   for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++)
         cout << board[i][j] << " ";
         cout << endl;
   }
}
bool isValid(int board[N][N], int row, int col) {
   for (int i = 0; i < col; i++) //check whether there is queen in the left or not
      if (board[row][i])
         return false;
   for (int i=row, j=col; i>=0 && j>=0; i--, j--)
      if (board[i][j]) //check whether there is queen in the left upper diagonal or not
         return false;
   for (int i=row, j=col; j>=0 && i<N; i++, j--)
      if (board[i][j]) //check whether there is queen in the left lower diagonal or not
         return false;
   return true;
}
bool solveNQueen(int board[N][N], int col) {
   if (col >= N) //when N queens are placed successfully
      return true;
   for (int i = 0; i < N; i++) { //for each row, check placing of queen is possible or not
      if (isValid(board, i, col) ) {
         board[i][col] = 1; //if validate, place the queen at place (i, col)
         if ( solveNQueen(board, col + 1)) //Go for the other columns recursively
            return true;
         board[i][col] = 0; //When no place is vacant remove that queen
      }
   }
   return false; //when no possible order is found
}
bool checkSolution() {
   int board[N][N];
   for(int i = 0; i<N; i++)
   for(int j = 0; j<N; j++)
   board[i][j] = 0; //set all elements to 0
   if ( solveNQueen(board, 0) == false ) { //starting from 0th column
      cout << "Solution does not exist";
      return false;
   }
   printBoard(board);
   return true;
}
int main() {
   checkSolution();
}