题目

#include<bits/stdc++.h>
using namespace std;
string s;
char base[100]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
int main(){
    cin>>s;
    int len=s.size();string sum="";
//    cout<<s<<endl;
    for(int i=0;i<(len-len%3);i+=3){
    	int a=s[i],b=s[i+1],c=s[i+2];
		int x=a/4,y=(a%4)*16+b/16,z=(b%16)*4+c/64,u=c%64;
		sum+=base[x]+base[y]+base[z]+base[u];
    }
//    cout<<sum<<endl;
	if(len%3==1){
		int a=s[len-1];
		int x=a/4,y=a%4*16;
		sum+=base[x]+base[y]+"==";
	}
	if(len%3==2){
		int a=s[len-2],b=s[len-1];
		int x=a/4,y=a%4*16+b/16,z=b%16*4;
		sum+=base[x]+base[y]+base[z]+"=";
	}
	cout<<sum;
	return 0;
}