Leetcode 415. Add Strings[easy]

题目：
Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

The length of both num1 and num2 is < 5100.
Both num1 and num2 contains only digits 0-9.
Both num1 and num2 does not contain any leading zero.
You must not use any built-in BigInteger library or convert the inputs to integer directly.

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开启leetcode数学专题。
刚起床，20分钟上课，切一个水题。
没啥说的，最简单的高精度加法。

class Solution {public:    string addStrings(string num1, string num2) {        string ans;        int n = num1.length();        int m = num2.length();        for (int i = 0; i < n / 2; i++)            swap(num1[i], num1[n - i - 1]);        for (int i = 0; i < m / 2; i++)            swap(num2[i], num2[m - i - 1]);        int jin = 0;        for (int i = 0; i < max(n, m); i++) {            if (i < n) jin += num1[i] - '0';            if (i < m) jin += num2[i] - '0';            ans.push_back(jin % 10 + '0');            jin = jin / 10;        }        if (jin) ans.push_back(jin + '0');        for (int i = 0; i < ans.length() / 2; i++)            swap(ans[i], ans[ans.length() - i - 1]);        return ans;    }};