题解 | #24点游戏算法#

java dfs

import java.util.*;
public class Main {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            while(sc.hasNextInt()) {
                double[] a = new double[4];
                for (int i = 0; i < 4; i++) {
                    a[i] = sc.nextInt();
                }
                 boolean[] visited = new boolean[4];
                Arrays.fill(visited, true);
                if (dfs(a, 0 , 0, visited)) {
                    System.out.println("true");
                } else {
                    System.out.println("false");
                }
            }
        }
                
            private static boolean dfs(double[] a, double res, int idex, boolean[] visited) {
                if (idex >= 4) {
                    return Math.abs(res - 24) == 0;
                }
                
                boolean flag = false;
                for(int i = 0; i< 4; i++) {
                    if (visited[i]) {
                        visited[i] = false;
                        flag = dfs(a, res + a[i] , idex+1, visited) ||  dfs(a, res - a[i] , idex+1, visited)|| dfs(a, res * a[i] , idex+1, visited)|| dfs(a, res / a[i] , idex+1, visited);
                        visited[i] = true;
                        if (flag == true) {
                            break;
                        }
                    }
                }
                return flag;
            }
}