Problem

Given two binary strings a and b, return their sum as a binary string.

Example 1:

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Input: a = "11", b = "1"
Output: "100"

Example 2:

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Input: a = "1010", b = "1011"
Output: "10101"

Constraints:

  • 1 <= a.length, b.length <= 10^4
  • a and b consist only of '0' or '1' characters.
  • Each string does not contain leading zeros except for the zero itself.

Solve

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class Solution:
    def addBinary(self, a: str, b: str) -> str:
      # s 用來存放結果 ，因為是用append(從後面加) 最後要用reversed
      s = []
      # carry 存放進位
      carry = 0
      i = len(a) - 1
      j = len(b) - 1

      # 運算式
      # 不會動到原先的a,b
      # i  j 為處理的位置
      while i >= 0 or j >= 0 or carry:
        total = carry
        if i >= 0:
          total += int(a[i])
          i -= 1
        if j >= 0:
          total += int(b[j])
          j -= 1
        s.append(str(total % 2))
        carry = total // 2
        
      return ''.join(reversed(s))

稍做修改

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class Solution:
    def addBinary(self, a: str, b: str) -> str:
      s = ""
      carry = 0
      i = len(a) - 1
      j = len(b) - 1

      while i >= 0 or j >= 0 or carry:
        total = carry
        if i >= 0:
          total += int(a[i])
          i -= 1 
        if j >= 0:
          total += int(b[j])
          j -= 1

        s += (str(total % 2))
        carry = total // 2

        
      return s[::-1]

偷吃步

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class Solution:
    def addBinary(self, a: str, b: str) -> str:
        x=int(a,2)
        y=int(b,2)
        return bin(x+y)[2:]