题解 | 高精度整数加法

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() {
    string s1;
    string s2;
    cin >> s1 >> s2;
    int maxlen = max(s1.length(), s2.length());
    string longstr, shortstr;
    vector<int> up(maxlen, 0);
    vector<int> down(maxlen, 0);
    if(maxlen == s1.length()){
        longstr = s1;
        shortstr = s2;
    }else {
        longstr = s2;
        shortstr = s1;
    }
    for(int i = 0; i < maxlen; i++){
        up[i] = longstr[i] - '0';
    }
    int t = maxlen - shortstr.length();
    for(int i = t; i < maxlen; i++){
        down[i] = shortstr[i - t] - '0';
    }
    // vector<int> res(maxlen + 1, 0);
    int n0 = 0;
    for(int i = maxlen - 1; i >= 0; i--){
        int x = up[i] + down[i];
        if(x < 10){
            up[i] = x;
            continue;
        }
        int a = x % 10;
        int b = x / 10;
        if(i == 0){
            n0 = b;
            up[i] = a;
        }else{
            up[i - 1] += b;
            up[i] = a;
        }
    }
    if(n0 != 0) cout << n0;
    for(int i = 0; i < maxlen; i++){
        cout << up[i];
    }

}
// 64 位输出请用 printf("%lld")