题解 | #Integer Inquiry#

#include <iostream>
#include <vector>
#include <cstring>

using namespace std;

string LongIntegerSum(const string& a, const string& b) {
    int maxLen = max(a.size(), b.size()) + 1;
    string res(maxLen, '0');
    res[maxLen] = '\0';

    int carry = 0;
    int i = a.size() - 1;
    int j = b.size() - 1;
    int k = maxLen - 1;

    while (i >= 0 || j >= 0 || carry == 1) {
        int sum = carry;
        if (i >= 0)
            sum += a[i--] - '0';
        if (j >= 0)
            sum += b[j--] - '0';

        if (sum > 9) {
            sum -= 10;
            carry = 1;
        }
        else {
            carry = 0;
        }

        res[k--] = sum + '0';
    }

    string result(res);
    size_t pos = result.find_first_not_of('0');
    if (pos != string::npos) {
        return result.substr(pos);
    }

    return "0";
}

int main() {
    string str;
    string output = "0";
    while (cin >> str) {
        if (str == "0") {
            cout << output << endl;
        }
        else {
            output = LongIntegerSum(output, str);
        }
    }

    return 0;
}