八皇后问题

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

public class Solution {

    public static int[][] chessboard = new int[8][8];
    public static List<String> solutionStrs = new ArrayList<>(); //每行的皇后列位置

    public static void findQueenPosition(int row) {
        if (row >= 8) {
            addSolution();
            return;
        }

        for (int col = 0; col < 8; col++) {
            if (isValid(row, col)) {
                chessboard[row][col] = 1;
                findQueenPosition(row + 1);
                chessboard[row][col] = 0;
            }
        }
    }

    public static boolean isValid(int row, int col) {
        for (int i = 0; i < row; i++) {
            if (chessboard[i][col] == 1) {
                return false;
            }
        }

        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
            if (chessboard[i][j] == 1) {
                return false;
            }
        }

        for (int i = row - 1, j = col + 1; i >= 0 && j <= 7; i--, j++) {
            if (chessboard[i][j] == 1) {
                return false;
            }
        }

        return true;
    }

    public static void addSolution() {
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 8; i++) {
            for (int j = 0; j < 8; j++) {
                if (chessboard[i][j] == 1) {
                    builder.append("col:").append(j).append(",");
                }
            }
        }
        solutionStrs.add(builder.toString());
    }

    public static String getChessboardTableFormat() {
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 8; i++) {
            for (int j = 0; j < 8; j++) {
                if (chessboard[i][j] == 1) {
                    builder.append("o ");
                } else {
                    builder.append("+ ");
                }
            }
            builder.append("\n");
        }
        builder.append("\n");

        return builder.toString();
    }

    public static void main(String[] args) {

        //开始寻找第0行皇后所在列的位置
        findQueenPosition(0);
        System.out.println("八皇后问题有 " + solutionStrs.size() + " 种解法");
    }
}

参考链接:https://www.jianshu.com/p/65c8c60b83b8

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