题解 | #高精度整数加法#

// 大数问题，用字符串来模拟加法运算，主要考虑进位情况
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;

int main() {
    string str1, str2;
    cin >> str1 >> str2;
    reverse(str1.begin(), str1.end());
    reverse(str2.begin(), str2.end());
    int len1 = str1.length();
    int len2 = str2.length();
    int carry = 0;
    string ans;
    int i = 0, j =0;
    for(; i < len1 && j < len2; i++,j++){
        int sum =  (str1[i] - '0') + (str2[j] - '0') + carry ;
        if( sum >= 10){
            carry = 1;
            ans += to_string(sum%10);
        }else{
            carry = 0;
            ans += to_string(sum);
        }
    }

    for(; i < len1; i++){
        int sum =  (str1[i] - '0') + carry ;
        if( sum >= 10){
            carry = 1;
            ans += to_string(sum%10);
        }else{
            carry = 0;
            ans += to_string(sum);
        }
    }

    for(; j < len2; j++){
        int sum =  (str2[j] - '0') + carry ;
        if( sum >= 10){
            carry = 1;
            ans += to_string(sum%10);
        }else{
            carry = 0;
            ans += to_string(sum);
        }
    }
    
    if(carry){
        ans += to_string(carry);
    }

    reverse(ans.begin(), ans.end());
    cout << ans << endl;
    return 0;
}
// 64 位输出请用 printf("%lld")