题解 | 大数加法

#include <algorithm>
#include <iterator>
#include <ostream>
#include <string>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 计算两个数之和
     * @param s string字符串 表示第一个整数
     * @param t string字符串 表示第二个整数
     * @return string字符串
     */
    string solve(string s, string t) {
        // write code here
        int carry = 0;
        string res;
        auto s_it = s.rbegin();
        auto t_it = t.rbegin();
    
        res.resize(max(s.size(), t.size()));
        auto res_it = res.rbegin();

        while (s_it != s.rend() && t_it != t.rend()) {
            int sum = *s_it - '0' + *t_it - '0' + carry;
            *res_it = (char)((sum % 10) + '0');
            carry = sum >= 10 ? 1 : 0;

            s_it++;
            t_it++;
            res_it++;
        }

        auto new_it = s_it == s.rend() ? t_it : s_it;
        auto new_end = s_it == s.rend() ? t.rend() : s.rend();

        while (new_it != new_end) {
            int sum = *new_it - '0' + carry;
            *res_it = (char)((sum % 10) + '0');
            carry = sum >= 10 ? 1 : 0;

            res_it++;
            new_it++;
        }

        if (carry) {
            res.insert(0, "1");
        }

        return res;
    }
};