add-binary.js

// Description:
// Given two binary strings a and b, return their sum as a binary string.

// Example 1:
// Input: a = "11", b = "1"
// Output: "100"

// Example 2:
// Input: a = "1010", b = "1011"
// Output: "10101"

// Constraints:
// 1 <= a.length, b.length <= 104
// a and b consist only of '0' or '1' characters.
// Each string does not contain leading zeros except for the zero itself.

// my solution:
var addBinary = function (a, b) {
  let carry = 0;
  let result = "";

  let i = a.length - 1;
  let j = b.length - 1;

  while (i >= 0 || j >= 0 || carry > 0) {
    const digitA = i >= 0 ? parseInt(a[i]) : 0;
    const digitB = j >= 0 ? parseInt(b[j]) : 0;

    const sum = digitA + digitB + carry;
    const digitSum = sum % 2;
    carry = Math.floor(sum / 2);

    result = digitSum + result;

    i--;
    j--;
  }

  return result;
};