67.Add Binary

[niuworld]

Question:

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

Solution:

class Solution {
public:
    string addBinary(string a, string b) {
      int alen = a.length();
      int blen = b.length();
      if( alen <  blen ){
          swap(a, b);
          swap(alen, blen);
      }

      int minus = alen - blen;
      if( minus != 0){
          while( minus !=0 ){
              b = "0" + b ;
              minus--;
          }
      }
      string result;
      int carry = 0, atem , btem;
      int pos = alen - 1;
      while( pos >= 0){
       atem = a[pos] - '0';
       btem = b[pos] - '0';
      int sum = atem + btem + carry ;
      int res = sum % 2 ;
       carry = sum / 2 ;
      char re = res + '0';
      result = re + result;
      pos--;
      }
      if ( carry == 1)
      result = "1" + result;
      return result;
    }
};