# Program for Implementation of N-Queen problem in Java

The n queens puzzle is the problem of placing eight chess queens on an n×n chessboard so that no two queens threaten each other. Thus, a solution requires that no two queens share the same row, column, or diagonal.

```//program for Implementation of n-queen problem
import java.io.*;
import java.util.*;
import java.lang.*;
class Queen {
int x[] = new int[20];
void NQueen(int k, int n) {
int i;
for (i = 0; i < n; i++) {
if (place(k, i) == 1) {
x[k] = i;
if (k == n)
display(x, n);
else
NQueen(k + 1, n);

}
}
}
public int place(int k, int i) {
for (int j = 1; j <= k - 1; j++) {
if ((x[j] == i) || (Math.abs(x[j] - i) == Math.abs(j - k)))
return 0;
}
return 1;
}

void display(int[] x, int n) {
char[][] p;
p = new char[n + 1][n + 1];
for (int i = 0; i <= n; i++) {
for (int j = 0; j <= n; j++) {
p[i][j] = '*';
}
}
int j = 0;
for (int i = 1; i <= n; i++)
p[j++][x[i]] = 'Q';

for (int i = 0; i < n; i++) {
for (int k = 0; k < n; k++) {
System.out.print(" " + p[i][k]);

}
System.out.println(" ");

}
System.out.println("*********************************** ");
}
}
class QueenDemo {
public static void main(String args[])
throws IOException {
System.out.println("Enter the no.of queens required");
Queen q = new Queen();
q.NQueen(1, n);

}
}
/* output::

Enter the no.of queens required
4
* Q * *
* * * Q
Q * * *
* * Q *
***********************************
* * Q *
Q * * *
* * * Q
* Q * *
***********************************
Process Exit...
*/
```

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