题解 | #24点游戏算法#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    static boolean exist = false;
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[] nums = new int[4];
        nums[0] = in.nextInt();
        nums[1] = in.nextInt();
        nums[2] = in.nextInt();
        nums[3] = in.nextInt();

        boolean[] used = new boolean[4];
        dfs(nums, used, 0, 0);
        System.out.print(exist);
    }

    private static void dfs(int[] nums, boolean[] used, double target, int index) {
        if (index == 4) {
            if (target == 24) {
                exist = true;
            }
            return;
        }

        for (int i = 0; i < 4; i++) {
            if (!used[i]) {
                used[i] = true;
                dfs(nums, used, target + nums[i], index + 1);
                dfs(nums, used, target - nums[i], index + 1);
                dfs(nums, used, target * nums[i], index + 1);
                dfs(nums, used, target / nums[i], index + 1);
                used[i] = false;
            }
        }
    }
}