[LeetCode] 415. Add Strings

轉自 LeetCode

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.

<Solution>

We have to convert the string to number by ourself because we can not use atoi or stoi. The simplest way is to subtract ‘0’ and store the difference.

Thoughts as following:

• Start from the end of each string
• If the length of string is not enough, value will be 0
• Calculate the carry digit
• If the carry digit is not 0 in the end, then add ‘1’ in the front of string.

Solution as following