题解 | #24点游戏算法#

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[] nums=new int[4];
        if (in.hasNext()) { 
            String[] str = in.nextLine().split(" ");
            for(int i=0;i<4;i++)nums[i]=Integer.parseInt(str[i]);
        }
	  //先确定四个数字的顺序
        for(int a=0;a<4;a++){
            int used=(1<<a);
            for(int b=0;b<4;b++){
                if(((used>>b) & 1)==1)continue;
                used= (used|(1<<b));
                for(int c=0;c<4;c++){
                    if(((used>>c) & 1)==1)continue;
                    used= (used|(1<<c));
                    for(int d=0;d<4;d++){
                        if(((used>>d) & 1)==1)continue;
                        if(func(nums[a],nums[b],nums[c],nums[d])){
                            System.out.println("true");
                            return;
                        }
                    }
                }
            }
        }
        System.out.println("false");
    }
    public static boolean func(int aa,int bb,int cc,int dd){
        char[] all={'+','-','*','/'};
        double a=aa,b=bb,c=cc,d=dd;
	  	//计算，有以下4中计算方式
        // ab cd ; ab c d ; a bc d ; a b cd ;
        for(char ch1:all){
            double x1=calu(a,b,ch1);
            double z1=calu(b,c,ch1);
            double u1=calu(c,d,ch1);
            for(char ch2:all){
                double x2=calu(c,d,ch2);
                double y2=calu(x1,c,ch2);
                double z2=calu(a,z1,ch2);
                double u2=calu(b,u1,ch2);
                for(char ch3:all){
                    double x3=calu(x1,x2,ch3);
                    if(x3==24)return true;
                    double y3=calu(y2,d,ch3);
                    if(y3==24)return true;
                    double z3=calu(z2,d,ch3);
                    if(z3==24)return true;
                    double u3=calu(a,u2,ch3);
                    if(u3==24)return true;
                }
            }
        }
        return false;
    }
    public static double calu(double a,double b,char ch){
        double res=0;
        switch(ch){
            case '+':
                res=a+b;
                break;
            case '-':
                res=a-b;
                break;
            case '*':
                res=a*b;
                break;
            case '/':
                if(b==0)res=10001;
                else res=a/b;
        }
        return res;
    }
}

理论上各种情况都考虑到了