67. Add Binary

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"

Runtime: 64 ms, faster than 48.07% of JavaScript online submissions for Add Binary.

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
    const lenA = a.length;
    const lenB = b.length;
    let i = lenA - 1;
    let j = lenB - 1;
    let carry = 0;
    const result = [];
    while(i >= 0 || j >= 0) {
        if (a[i] === '1' && b[j] === '1') {
            result.push(carry);
            carry = 1;
        } else if (a[i] === '0' && b[j] === '0') {
            result.push(carry);
            carry = 0;
        } else if ((a[i] === '1' && b[j] !== '1') || (a[i] !== '1' && b[j] === '1')) {
            if (carry) {
                result.push(0);
            } else {
                result.push(1);
            }
        } else {
            result.push(carry);
            carry = 0;
        }
        i--;
        j--;
    }
    if (carry) {
        result.push(carry);
    }
    return result.reverse().join('');
};

Runtime: 60 ms, faster than 98.45% of JavaScript online submissions for Add Binary.

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
    const lenA = a.length;
    const lenB = b.length;
    let i = lenA - 1;
    let j = lenB - 1;
    let carry = 0;
    let result = '';
    while(i >= 0 || j >= 0) {
        if (a[i] === '1' && b[j] === '1') {
            result = carry + result;
            carry = 1;
        } else if (a[i] === '0' && b[j] === '0') {
            result = carry + result;
            carry = 0;
        } else if ((a[i] === '1' && b[j] !== '1') || (a[i] !== '1' && b[j] === '1')) {
            if (carry) {
                result = '0' + result;
            } else {
                result = '1' + result;
            }
        } else {
            result = carry + result;
            carry = 0;
        }
        i--;
        j--;
    }
    if (carry) {
        result = carry + result;
    }
    return result;
};