content: 
  /* Java program to solve N Queen Problem using
     backtracking */
     public class NQueenProblem {
      final int N = 4;
    
      /* A utility function to print solution */
      void printSolution(int board[][])
      {
          for (int i = 0; i < N; i++) {
              for (int j = 0; j < N; j++) 
                  System.out.print(" " + board[i][j]
                                   + " ");
              System.out.println();
          }
      }
    
      /* A utility function to check if a queen can
         be placed on board[row][col]. Note that this
         function is called when "col" queens are already
         placeed in columns from 0 to col -1. So we need
         to check only left side for attacking queens */
      boolean isSafe(int board[][], int row, int col)
      {
          int i, j;
    
          /* Check this row on left side */
          for (i = 0; i < col; i++)
              if (board[row][i] == 1)
                  return false;
    
          /* Check upper diagonal on left side */
          for (i = row, j = col; i >= 0 && j >= 0; i--, j--)
              if (board[i][j] == 1)
                  return false;
    
          /* Check lower diagonal on left side */
          for (i = row, j = col; j >= 0 && i < N; i++, j--)
              if (board[i][j] == 1)
                  return false;
    
          return true;
      }
    
      /* A recursive utility function to solve N
         Queen problem */
      boolean solveNQUtil(int board[][], int col)
      {
          /* base case: If all queens are placed
             then return true */
          if (col >= N)
              return true;
    
          /* Consider this column and try placing
             this queen in all rows one by one */
          for (int i = 0; i < N; i++) {
              /* Check if the queen can be placed on
                 board[i][col] */
              if (isSafe(board, i, col)) {
                  /* Place this queen in board[i][col] */
                  board[i][col] = 1;
    
                  /* recur to place rest of the queens */
                  if (solveNQUtil(board, col + 1) == true)
                      return true;
    
                  /* If placing queen in board[i][col]
                     doesn't lead to a solution then
                     remove queen from board[i][col] */
                  board[i][col] = 0; // BACKTRACK
              }
          }
    
          /* If the queen can not be placed in any row in
             this column col, then return false */
          return false;
      }
    
      /* This function solves the N Queen problem using
         Backtracking.  It mainly uses solveNQUtil () to
         solve the problem. It returns false if queens
         cannot be placed, otherwise, return true and
         prints placement of queens in the form of 1s.
         Please note that there may be more than one
         solutions, this function prints one of the
         feasible solutions.*/
      boolean solveNQ()
      {
          int board[][] = { { 0, 0, 0, 0 },
                            { 0, 0, 0, 0 },
                            { 0, 0, 0, 0 },
                            { 0, 0, 0, 0 } };
    
          if (solveNQUtil(board, 0) == false) {
              System.out.print("Solution does not exist");
              return false;
          }
    
          printSolution(board);
          return true;
      }
    
      // driver program to test above function
      public static void main(String args[])
      {
          NQueenProblem Queen = new NQueenProblem();
          Queen.solveNQ();
      }
  } 