y总写法

/*
Author: SJ
*/
#include <bits/stdc++.h>
using namespace std;
string s1, s2;
vector<int> a, b, c;
vector<int> add(vector<int> &a, vector<int> &b) {
    int tmp = 0;
    for (int i = 0; i < a.size() || i < b.size(); i++) {
        if (i < a.size()) tmp += a[i];
        if (i < b.size()) tmp += b[i];
        c.push_back(tmp % 10);
        tmp /= 10;
    }

    if (tmp) c.push_back(tmp);

    return c;
}
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    cin >> s1 >> s2;
    for (int i = 0; i < s1.size(); i++) a.push_back(s1[s1.size() - i - 1] - '0');
    for (int i = 0; i < s2.size(); i++) b.push_back(s2[s2.size() - i - 1] - '0');
    c = add(a, b);
    for (int i = c.size() - 1; i >= 0; i--) cout << c[i];
    return 0;
}

我的不用STL的写法

/*
Author: SJ
*/
#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int a[N], b[N], c[N];
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    string s1, s2;
    cin >> s1 >> s2;
    for (int i = 0; i < s1.size(); i++) a[i] = s1[s1.size() - i - 1] - '0';
    for (int i = 0; i < s2.size(); i++) b[i] = s2[s2.size() - i - 1] - '0';

    int tmp = max(s1.size(), s2.size());
    for (int i = 0; i < 2 * tmp; i++) {
        c[i] += a[i] + b[i];
        if (c[i] >= 10) {
            c[i + 1] += c[i] / 10;
            c[i] %= 10;
        }
    }

    int mark = 2 * tmp;
    for (; mark > 0; mark--) if (c[mark]) break;
    for (; mark >= 0; mark--) cout << c[mark];
    return 0;
}

不开O2的话速度差异明显，开O2的话好像没有差别