Add Binary

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

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

class Solution {public:string addBinary(string a, string b) {int la = a.length();int lb = b.length();int shorter = la > lb ? (la - lb) : (lb - la);string s(shorter,'0');if(la > lb) b = s + b;else a = s + a;int carry = 0;for(int i = a.length() - 1; i >= 0; --i){int sum = a[i] - '0' + b[i] - '0' + carry;carry = sum >> 1;a[i] = sum % 2 + '0';}if(carry)a = "1" + a;return a;}};