67. Add Binary

[jzhangnu]

var addBinary = function(a, b) {
    var lena = a.length - 1,
        lenb = b.length - 1,
        res = [],
        count = 0;

    while(lena >= 0 || lenb >= 0 || count > 0){
        var va = 0,
            vb = 0;

        if(lena >= 0){
            a.charAt(lena) === '0' ? va = 0 : va = 1;
            lena--;
        }

        if(lenb >= 0){
            b.charAt(lenb) === '0' ? vb = 0 : vb = 1;
            lenb--;
        }

        if(va+vb+count > 1){
            var digit = (va+vb+count - 2);
            res.push(digit);
            count = 1;
        }else {
            res.push(va+vb+count);
            count = 0;
        }

    }
    //while
    return res.reverse().join('').toString();
};