Binary Sum

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.

Write your solution:

function main (a, b) {
    return;
}

function main (a, b) { return; }

Test Case 1

Input: "11", "1"
Output: "100"

Test Case 2

Input: "1010", "1011"
Output: "10101"

Solution

Complexity:

• Time complexity: O(n).
• Space complexity: O(1).

function sum(a, b) {
    const len1 = a.length;
    const len2 = b.length;
    const max = Math.max(len1, len2);
    let carry = 0;
    let val = 0;
    let res = '';

    for (let i = 0; i < max; i++) {
        val = Number(a[len1 - 1 - i] || 0) + Number(b[len2 - 1 - i] || 0) + carry;
        carry = Math.floor(val / 2);
        res = (val % 2) + res;
    }

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

    return res;
}