we could be doing space complexity O(1) if in Js was possible to replace char in
the string by index without creating a new string..
<pre class="shiki github-dark shaku"><code>/** * @param {string} num1 * @param {string} num2 * @return {string} */function add(num1, num2) { let x = num1.length - 1 let y = num2.length - 1 let remainder = 0 let result = '' while (x &gt;= 0 || y &gt;= 0 || remainder) { let sum = Number(num1[x] || 0) + Number(num2[y] || 0) + remainder remainder = 0 if (sum &gt; 9) { result = (sum - 10) + result remainder = 1 } else { result = sum + result } x-- y-- } return result }</code></pre>

This is my accepted solution(time&space complexity in worse case both max(num1, num2))

Luckily we have BigInt in JavaScript so handle big numbers. What if we need to do it by ourselves for older browsers? You are asked to implement a str…