Given two non-negative numbers 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.

 

 

我的第一个想法就是选好两个字符串，然后模拟加法进位，然后用一个字符串接着，同时记住进位，最后返回这个字符串的反转即可。

 

没有想到什么比较好的解决思路

public class Solution {    public String addStrings(String num1, String num2) {        StringBuilder sb = new StringBuilder();        int carry = 0;        for(int i = num1.length() - 1, j = num2.length() - 1; i >= 0 || j >= 0; i--, j--){            int x = i < 0 ? 0 : num1.charAt(i) - '0';            int y = j < 0 ? 0 : num2.charAt(j) - '0';            sb.append((x + y + carry) % 10);            carry = (x + y + carry) / 10;        }        if(carry != 0)            sb.append(carry);        return sb.reverse().toString();    }}