lc415. Add Strings

2022-01-26 226 words 2 minutes

Contents

Given two non-negative integers, num1 and num2 represented as string, return the sum of num1and num2 as a string.

You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly.

Example 1:

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Input: num1 = "11", num2 = "123"
Output: "134"

Example 2:

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Input: num1 = "456", num2 = "77"
Output: "533"

Example 3:

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Input: num1 = "0", num2 = "0"
Output: "0"

Constraints:

1 <= num1.length, num2.length <= 104
num1 and num2 consist of only digits.
num1 and num2 don’t have any leading zeros except for the zero itself.

解题思路：

这道题限制not convert the inputs to integers directly，所以我们只能按照每一步来模拟进位计算。

把两个字符串反向。
把每一位变成数字，模拟进位计算

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class Solution(object):
    def addStrings(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        ans=''
        _up=0
        while len(num1)>0 and len(num2)>0:
            _1=int(num1[-1])
            _2=int(num2[-1])
            num1=num1[:-1]
            num2=num2[:-1]
            _sum=_1+_2+_up
            if _sum>9:
                _up=1
            else:
                _up=0
            ans+=str(_sum%10)
        num=''
        if len(num1)>0:
            num=num1
        elif len(num2)>0:
            num=num2
        while len(num)>0:
            _1=int(num[-1])
            num=num[:-1]
            _sum=_1+_up
            if _sum>9:
                _up=1
            else:
                _up=0
            ans+=str(_sum%10)
        if _up==1:
            ans+='1'
        return ans[::-1]

注意如果最后_up还是1，那么记得在最终答案上补上1.

执行用时：36 ms, 在所有 Python 提交中击败了41.44%的用户

内存消耗：13.3 MB, 在所有 Python 提交中击败了43.47%的用户