N-Queens

1import java.util.Arrays;
2 
3public class Main {
4    private final int size;
5    private final int[] queens;
6 
7    public Main(int size) {
8        this.size = size;
9        this.queens = new int[size];
10        Arrays.fill(queens, -1);
11    }
12 
13    private boolean isSafe(int row, int col) {
14        for (int previousRow = 0; previousRow < row; previousRow++) {
15            int previousCol = queens[previousRow];
16            if (previousCol == col || Math.abs(previousCol - col) == row - previousRow) return false;
17        }
18        return true;
19    }
20 
21    public boolean solve(int row) {
22        if (row == size) return true;
23        for (int col = 0; col < size; col++) {
24            if (isSafe(row, col)) {
25                queens[row] = col;
26                if (solve(row + 1)) return true;
27                queens[row] = -1;
28            }
29        }
30        return false;
31    }
32 
33}