题解 | 24点游戏算法

import java.util.*;

import java.io.*;

public class Main {

    public static boolean judge = false;
    public static void main(String[]args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            double[]list = new double[4];
            for (int i = 0; i < 4; i++)
                list[i] = in.nextDouble();
            dfs(list, 4);
            System.out.println(judge);
        }
    }

    public static void dfs(double[]list, int n) {
        if (n < 2) {
            if (Math.abs( list[0] - 24) < 0.001) {
                judge = true;
            }
            return;
        }
        double[] list2 = new double[n - 1];
        for (int i = 0; i < n ; i++) {
            for (int j = 0; j < n; j++) {
                if (i != j) {
                    int u = 0;
                    for (int k = 0; k < n; k++) {
                        if (k != i && k != j) {
                            list2[u++] = list[k];
                        }
                    }
                    list2[u] = list[i] + list[j];
                    dfs(list2, n - 1);
                    list2[u] = list[i] - list[j];
                    dfs(list2, n - 1);
                    list2[u] = list[i] * list[j];
                    dfs(list2, n - 1);
                    if (list[j] != 0 ) {
                        list2[u] = list[i] / list[j];
                        dfs(list2, n - 1);
                    }
                }

            }
        }

    }
}