PHP中的八皇后问题算法实现步骤

<?php

class EightQueens {
    private $board; // 棋盘
    private $solutions; // 存放所有解的数组

    public function __construct() {
        $this->board = array_fill(0, 8, array_fill(0, 8, 0));
        $this->solutions = array();
    }

    public function solve() {
        $this->placeQueen(0);
        return $this->solutions;
    }

    private function placeQueen($row) {
        if ($row == 8) {
            $this->solutions[] = $this->board;
            return;
        }

        for ($col = 0; $col < 8; $col++) {
            if ($this->isSafe($row, $col)) {
                $this->board[$row][$col] = 1; // 放置皇后

                // 递归放置下一行的皇后
                $this->placeQueen($row + 1);

                $this->board[$row][$col] = 0; // 回溯
            }
        }
    }

    private function isSafe($row, $col) {
        // 检查当前列是否已有皇后
        for ($i = 0; $i < $row; $i++) {
            if ($this->board[$i][$col] == 1) {
                return false;
            }
        }

        // 检查左上对角线是否有皇后
        $i = $row - 1;
        $j = $col - 1;
        while ($i >= 0 && $j >= 0) {
            if ($this->board[$i][$j] == 1) {
                return false;
            }
            $i--;
            $j--;
        }

        // 检查右上对角线是否有皇后
        $i = $row - 1;
        $j = $col + 1;
        while ($i >= 0 && $j < 8) {
            if ($this->board[$i][$j] == 1) {
                return false;
            }
            $i--;
            $j++;
        }

        return true;
    }
}

// 使用示例
$eightQueens = new EightQueens();
$solutions = $eightQueens->solve();

foreach ($solutions as $solution) {
    foreach ($solution as $row) {
        echo implode(" ", $row) . "
";
    }
    echo "
";
}