add-binary.js

// Given two binary strings, return their sum (also a binary string).
//
// The input strings are both non-empty and contains only characters 1 or 0.
//
// Example 1:
//
//
// Input: a = "11", b = "1"
// Output: "100"
//
// Example 2:
//
//
// Input: a = "1010", b = "1011"
// Output: "10101"
//


/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
    var aLen = a.length,
        bLen = b.length,
        len = Math.max(aLen, bLen),
        results = new Array(len),
        c = 0;
    --aLen, --bLen, --len;
    var i, j;
    while (aLen >= 0 || bLen >= 0) {
        i = aLen >= 0 ? +a[aLen] : 0;
        j = bLen >= 0 ? +b[bLen] : 0;
        results[len] = i ^ j ^ c;
        c = i & j | c & (i ^ j);
        --aLen, --bLen, --len;
    }
    if (c) {
        results.unshift(1);
    }
    return results.join('');
};