Add Binary

 1 class Solution {
 2 public:
 3     string addBinary( string a, string b ) {
 4         int alen = a.length(), blen = b.length();
 5         string result( max( alen, blen ), ‘0‘ );
 6         int carry = 0, i = max( alen, blen );
 7         while( --i >= 0 ) {
 8             if( alen > 0 ) { --alen; carry += a[alen]-‘0‘; }
 9             if( blen > 0 ) { --blen; carry += b[blen]-‘0‘; }
10             result[i] += carry % 2;
11             carry /= 2;
12         }
13         if( carry ) { result.insert( 0, "1" ); }
14         return result;
15     }
16 };