415. Add Strings（第十周）

Description

Add Strings - LeetCode

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

Note:

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

Input: "0", "0"
Output: "0"

Solution

这个是要我们模拟平时手算加法的方法。我们可以从string的最后一位开始，从后往前加，如果某一个string已经遍历到了开头，那么就不用加上它。最后就是进位的问题，如果加到最后还有进位的话，那么就要把进位也放到结果中去。

至于结果，我们可以先顺序存放计算的结果，然后最后把他进行一次reverse操作即可得到答案

代码如下：

Source Code

submission

class Solution {public:    string addStrings(string num1, string num2) {        int i = num1.size() - 1;        int j = num2.size() - 1;        int carry = 0;        string res = "";        while (i >= 0 || j >= 0 || carry)        {            long sum = 0;            if (i >= 0)            {                sum += num1[i] - '0';                i--;            }            if (j >= 0)            {                sum += num2[j] - '0';                j--;            }            sum += carry;            carry = sum / 10;            sum = sum % 10;            res = res + to_string(sum);        }        reverse(res.begin(), res.end());        return res;    }};