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

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

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
    var alen = a.length || 0,
        blen = b.length || 0,
        res = "",
        carry = 0;
    if(alen < blen){
        var tmp = a;
        a = b;
        b = tmp;
        alen = a.length || 0;
        blen = b.length || 0;
    }

    for(var i = 1; i <= alen; i++){
        var _a = parseInt(a[alen - i]);
        var _b = parseInt(b[blen - i]) || 0;
        var add = _a + _b + carry;
        if(add === 3){
            res = "1" + res;
            carry = 1;
        }else if(add === 2){
            res = "0" + res;
            carry = 1;
        }else{
            res = add + res;
            carry = 0;
        }
    }

    if(carry === 1){
        res = "1" + res;
    }
    return res;
};