8 queen problem

gistfile1.txt

package com.algorithms;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class NQueen {
    class Position {
        int row;
        int col;

        public Position(int row, int col) {
            this.row = row;
            this.col = col;
        }

        public String toString() {
            return "[ " + row + "," + col + " ]";
        }
    }

    public List<List<String>> solveNQueens(int n) {
        List<List<String>> result = new ArrayList<>();
        Position[] positions = new Position[n];
        solve(0, positions, result, n);
        return result;
    }

    public void solve(int row, Position[] positions, List<List<String>> result, int n) {
        if (n == row) {
            StringBuffer buff = new StringBuffer();
            List<String> oneResult = new ArrayList<>();
            for (Position p : positions) {
                for (int i = 0; i < n; i++) {
                    if (p.col == i) {
                        buff.append("Q");
                    } else {
                        buff.append(".");
                    }
                }
                oneResult.add(buff.toString());
                buff = new StringBuffer();
            }
            buff.append("\n");
            result.add(oneResult);
            return;
        }

        for (int col = 0; col < n; col++) {
            boolean found = true;

            for (int queen = 0; queen < row; queen++) {
                if (positions[queen].col == col || positions[queen].col - positions[queen].row == col - row || positions[queen].row + positions[queen].col == col + row) {
                    found = false;
                    break;
                }
            }

            if (found) {
                positions[row] = new Position(row, col);
                solve(row + 1, positions, result, n);
            }
        }
    }
}