415_字符串相加

类型：字符串

• 415. 字符串相加 💚

  https://leetcode-cn.com/problems/add-strings/

  ❓ 给定两个字符串形式的非负整数 num1 和num2 ，计算它们的和。

  💡 模拟

  class Solution:
      def addStrings(self, num1: str, num2: str) -> str:
          if not num1 and not num2:
              return ""
          elif not num1:
              return num2
          elif not num2:
              return num1
  
          sumStr = ""
          carry = 0
          i, j = len(num1) - 1, len(num2) - 1
          while i >= 0 or j >= 0 or carry > 0:
              val1 = int(num1[i]) if i >= 0 else 0
              val2 = int(num2[j]) if j >= 0 else 0
              i -= 1
              j -= 1
              unitSum = val1 + val2 + carry
              if unitSum >= 10:
                  unitSum -= 10
                  carry = 1
              else:
                  carry = 0
              sumStr = str(unitSum) + sumStr
          return sumStr

  时间复杂度：O(max(len(num1), len(num2))，空间复杂度：O(1)