[OpenJudge-NOI]算24 Dfs

代碼

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

double a[5];

int Dfs(int k){
    if(k==1){
        if(fabs(a[0]-24)<1e-6){
            return 1;
        }else {
            return 0;
        }
    }else{
        double x,y;
        for(int i=0;i<k;i++){
            for(int j=i+1;j<k;j++){
                x=a[i];y=a[j];
                a[j]=a[k-1];
                for(int z=1;z<=6;z++){
                    if(z==1){
                        a[i]=x+y;
                        if(Dfs(k-1)) return 1;
                    }else if(z==2){
                        a[i]=x-y;
                        if(Dfs(k-1)) return 1;
                    }else if(z==3){
                        a[i]=y-x;
                        if(Dfs(k-1)) return 1;
                    }else if(z==4){
                        a[i]=x*y;
                        if(Dfs(k-1)) return 1;
                    }else if(z==5){
                        if(fabs(y)>=1e-6){
                            a[i]=x/y;
                            if(Dfs(k-1)) return 1;
                        }
                    }else if(z==6){
                        if(fabs(x)>=1e-6){
                            a[i]=y/x;
                            if(Dfs(k-1))return 1;
                        }
                    }
                }
                a[i]=x;a[j]=y;
            }
        }
    }
    return 0;
}

int main(){
    memset(a,0,sizeof a);
    while(scanf("%lf%lf%lf%lf",&a[0],&a[1],&a[2],&a[3])!=EOF){      
        if(a[0]==0&&a[1]==0&&a[2]==0&&a[3]==0){
            return 0;
        }
        int f=Dfs(4);
        if(f)cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
        memset(a,0,sizeof a);
    }
}