[leetcode] 415. Add Strings @ python

版权声明：版权归个人所有，未经博主允许，禁止转载 https://blog.csdn.net/danspace1/article/details/86556709

原题

Given two non-negative integers 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.

解法

定义一个函数, 将string转化为int, 我们遍历字符串, 使用ord函数计算每个数字跟’0’的距离. 最后将int转化为string.
Time: 2*O(n)
Space: O(1)

代码

class Solution(object):
    def addStrings(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        return str(self.stringToInt(num1) + self.stringToInt(num2))
    
    def stringToInt(self, s):
        ans = 0
        for i in range(len(s)):
            ans += (ord(s[i]) - ord('0'))*10**(len(s) - 1 - i)
        return ans