PAT乙級 1048. 數字加密(20)

坑：a、b 不一樣長的話，前端補0，補齊，統一爲較長的長度

//PAT-1-1048
#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

int main(){
    string a,b;
    cin>>a>>b;
    int flag=1;
    int len1=a.length();
    int len2=b.length();
    int len=len1<len2?len2:len1;
    //短補齊，統一爲一樣的長度
    while (len1<len) {
        len1++;
        a.insert(a.begin(),'0');
    }
    while (len2<len) {
        len2++;
        b.insert(b.begin(),'0');
    }
    
    for (int i=0; i<len; i++) {
        if (flag) {
            int re=0;
            re=(b[len2-i-1]-'0'+a[len1-i-1]-'0')%13;
            if (re<10) {
                b[len2-i-1]=re+'0';
            }else if(re==10) {
                b[len2-i-1]='J';
            }else if(re==11) {
                b[len2-i-1]='Q';
            }else if(re==12) {
                b[len2-i-1]='K';
            }
            flag=0;
            continue;
        }else{
            int re=0;
            re=(b[len2-i-1]-a[len1-i-1]);
            if (re<0) {
                re+=10;
            }
            b[len2-i-1]=re+'0';
            flag=1;
            continue;
        }
    }
    cout<<b<<endl;
    return 0;
}