ChatGPT is here - Use that to stop asking LeetCode questions during interviews

Posted on Thu 15 December 2022 in Jobs


I have interviewed a lot of software engineers looking for a new position. I've talked with college students looking for an internship, junior engineers just getting started, staff engineers looking for a new role, managers and directors to lead these teams. In every one of those interviews, I'd told the candidate that I hate puzzle questions (ie. "How many windows are in Seattle?") and I hate LeetCode style questions.

It turns out that ChatGPT is good at solving these problems.

Good. Maybe that will kill LeetCode interview questions once and for all. There are so many better ways to determine if an engineer is the right fit.

ChatGPT vs LeetCode

We have temporarily banned ChatGPT over on Stack Overflow, because it can and does provide subtly incorrect answers. It's been so bad that we called up two new moderators from the previous election today. One of my mod colleagues provided some context around this today too.

We get a few hundred CGPT flags per day, leading to hundreds or even thousands of post deletions per day. There's often one flag per user (not accounting overlap from several users), but each flag can lead to anywhere between a couple and tens of deletions per user.

LeetCode, however, checks your answer right away. They don't have the same problem as Stack Overflow. I wanted to see just how good this new chatbot was, and took it for a spin against a random LeetCode problem.

I randomly selected a medium difficulty problem with a 58% acceptance rate. My victim question: 1143. Longest Common Subsequence

Getting started

The first step in passing this test, is selecting the entire prompt, copying it and pasting it directly into LeetCode's UI. I didn't read the prompt and I didn't format it. Just a blind copy and paste. I also provided one instruction:

Provide python code

Press enter and wait 30 seconds or so.

The response

Within seconds I was provided this block of code

def longestCommonSubsequence(text1: str, text2: str) -> int:
    # Convert text1 and text2 to lists of characters
    s1 = list(text1)
    s2 = list(text2)

    # Initialize the dynamic programming table
    n = len(s1)
    m = len(s2)
    dp = [[0] * (m + 1) for _ in range(n + 1)]

    # Fill the dynamic programming table
    for i in range(1, n+1):
        for j in range(1, m+1):
            if s1[i-1] == s2[j-1]:
                dp[i][j] = dp[i-1][j-1] + 1
                dp[i][j] = max(dp[i-1][j], dp[i][j-1])

    # Return the length of the longest common subsequence
    return dp[n][m]

It likes the phrase "dynamic programming table". Along with this code, it even explains its reasoning for going this route. Maybe our intrepid AI can teach a junior dev a new trick or two while doing this puzzle.

ChatGPT explains its code ChatGPT explains its algorithm

Then it shows that tests pass...very confidently.

All the tests passed, so this implementation is correct

The result

I'm trying to show that ChatGPT can do this, so at this point I haven't read the prose above. I copy and pasted the code it returned and clicked "Submit".

I waited a few seconds for all tests to run and got my results.

ChatGPT beats over 96% of other implementations in runtime performance and 71% in memory performance

ChatGPT crushed this. It performs better than 96% of other submissions in terms of run time performance. It uses less memory than 71% of other submissions.

Can we please stop using LeetCode now?

The total time it took to perform this test was under 5 minutes. I randomly selected a problem, copy and pasted the prompt, waited for a response from the chatbot, copy and pasted the code response, waited for the tests to run. Complete.

As a hiring manager, I'd have wasted my time and the candidates time having them do this problem now. Instead, we can talk about an actual problem they will be solving. We can do a real world problem instead this. There are better ways to interview an engineer and I'm hoping ChatGPT makes that abundantly clear to hiring managers everywhere.

We're going to have to adapt our hiring processes, but that's a good thing. My recent experience shows that at most companies, it's bad anyway. Now we have an opportunity to shine some sunlight on it and make it better.

In the meantime, if you continue to use LeetCode or something similar to evaluate your candidate's technical skills, your are doing your team a huge diservice. Candidates know about this tool, and they know that the easiest way to get an interview is to play the game. There have been tens of thousands of layoffs in the tech industry in the last six months. I guarentee candidates are looking for every advantage they can get, to move to their next role.

- is a father, an engineer and a computer scientist. He is interested in online community building, tinkering with new code and building new applications. He writes about his experiences with each of these.