leetcode 415. Add Strings

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.

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class Solution(object):     def addStrings(self, num1, num2):         """         :type num1: str         :type num2: str         :rtype: str         """         """         "1234"+num2        "99678" num1        -------        100912                """         i, j = len(num1)-1, len(num2)-1         c = 0         ans = []         while i>=0 or j>=0 or c>0:             d1, d2 = 0, 0             if i>=0:                 d1 = int(num1[i])                 i -= 1             if j>=0:                 d2 = int(num2[j])                 j -= 1             s = d1+d2+c             c = s/10             ans.append(str(s%10))         return "".join(ans[::-1])

 使用if 判断绕过重复的while循环。