算24

http://bailian.openjudge.cn/practice/2787/submit/


ANS: 
//my answer
//输入部分表达不清楚  //结果显示wrong ans



#include <iostream>
#include <cmath>
using namespace std;

double a[5];
string s;
const double d = 1e-10;

bool isZero(double n){
    return fabs(n) < d;
}


bool count24(double a[], int n){
    if(n==1){
        if(isZero(a[0]-24)){//return value of 24 --> successful
            return true;
        }else{
            return false;
        }
    }
    
    double b[5];//store rest variables
    
    //get random 2 variables use random one of four operations
    for(int i = 0; i<n; i++){
        for(int j=i+1; j<n; j++){
            int n_rest = 0;
            
            for(int w = 0; w<n; w++){
                if(w!=i && w!=j){
                    b[n_rest++] = a[w];
                    
                }
            }
            
            
            //+
            b[n_rest] = a[i] + a[j];
            if(count24(b, n_rest+1))
                return true;
            
            
            //- //two conditions
            b[n_rest] = a[i] - a[j];//Update value of b[m]
            if(count24(b,n_rest+1))
                return true;
            
            b[n_rest] = a[j] - a[i];
            if(count24(b, n_rest+1))
                return true;
            
            
            //*
            b[n_rest] = a[i]*a[j];
            if(count24(b, n_rest+1))
                return true;
            
            
            //÷ //two conditions
            if(!isZero(a[j])){//not zero for division
                b[n_rest] = a[i]/a[j];
                if(count24(b, n_rest+1))
                    return true;
            
            }
            
            if(!isZero(a[i])){
                b[n_rest] = a[j]/a[i];
                if(count24(b,n_rest+1))
                    return true;
            }
        }
    }
    return false;
}

int main(){
    while(1){
        getline(cin,s);//string 遇到空格会结束 所以不用cin>>s, 用getline(cin,s);
        int j = 0;
        for(int i=0; i<s.length(); i++)
        {
            if(isdigit(s[i])){
                    a[j] = s[i]-'0';//string to int
                    j++;
            
            }
        }
        
        
        bool b = 1;
        for(auto &r : a){
             b &= isZero(r);
        }
        if(b){//Stop
            break;
        }
        
        //Not stop //process the variables
        if(count24(a,4))//has found
            cout<<"Yes"<<endl;
        else
            cout<<"No"<<endl;
        
        
    }
    
    return 0;
}


//换了输入方式后ok



//提供的答案
#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
double a[5];
#define EPS 1e-6   
//因为两数相除可能为小数 而浮点型是不能直接用 == 进行比较的 所以用两数的差的绝对值与13-6进行比较小于则相等 
bool isZero(double x)
{
	return fabs(x) <= EPS;
}
bool count24(double a[], int n)
{
    double b[5];
	//当数组a里面的元素只剩一个的时候 对a[0]进行判断 
	if(n == 1)
	{
		if(isZero(a[0] - 24))
			return true;
		else 
		    return false;
	}
	else{
		for(int i = 0; i < n-1; i++){   //任选两数进行枚举 
			for(int j = i+1; j < n; j++){
				int m = 0;
				for(int k = 0;k < n;k++){
					if(k != i && k != j)   b[m++] = a[k];  //将剩余的数放入b数组 
				}
				b[m] = a[i] + a[j] ; //将两数加进行递归 
				if(count24(b,m+1))   
				      return true;
				b[m] = a[i] - a[j] ; //将两数差进行递归 
			    if(count24(b,m+1))   
				      return true;
				b[m] = a[j] - a[i] ; //将两数差进行递归 
				if(count24(b,m+1))   
				      return true;
				b[m] = a[j] * a[i] ; //将两数积进行递归 
				if(count24(b,m+1))  
				      return true;
	            if(a[i] != 0){      //将两数差进行递归 
	            	b[m] = a[j]/a[i];
	            	if(count24(b,m+1))   return true;
	            }	
				if(a[j] != 0){     //将两数差进行递归 
	            	b[m] = a[i]/a[j];
	            	if(count24(b,m+1))   return true;
	            }		 
			}
		}
		
	}
	return false ;
}
int main()
{
	int z = 0;
	while(1){
        for(int i =0 ;i < 4; ++i){
			cin >> a[i]; //自动省略空格读取
			if(a[i] == 0)  z++;//算是不是4个都是0
		}
		if(z == 4) break;
	    if(count24(a,4)){
    	   cout<<"YES"<<endl; 
        }
        else
           cout<<"NO"<<endl;
        z = 0;
	}
    return 0;
}