Strong Password Checker
A hard-tier problem at 15% community acceptance, tagged with String, Greedy, Heap (Priority Queue). Reported in interviews at Devtron and 2 others.
Strong Password Checker lands in the hard tier with a 14% acceptance rate and has been asked by Devtron, Wix, and Flipkart. It's the kind of problem that looks straightforward at first, add characters, remove characters, swap characters, but the trick is finding the minimum edits needed to satisfy all password rules at once. Most candidates waste time exploring every possible state instead of recognizing the greedy pattern. If this problem hits your live assessment and you blank on the sequence of repairs, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Strong Password Checker"
Strong Password Checker is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe trap is thinking you can solve this greedily for each rule independently. You can't. A single character insertion might fix both the length requirement and the repeating character constraint simultaneously, so you need to prioritize edits by their impact. The real insight is that when you're deleting repeating characters, you should target sequences whose length modulo 3 equals a specific value first, because those give you the maximum payoff. When inserting, you must insert into the longest repeating sequences. When replacing, any sequence works the same. The problem requires you to balance three competing constraints (length, variety, no repeats) and find the minimum total moves. Most solutions that fail either miss the modulo 3 optimization on deletions or handle insertions without properly reducing repeat counts. StealthCoder is your hedge when you hit this live and the pattern doesn't click immediately.
Pattern tags
You know the problem.
Make sure you actually pass it.
Strong Password Checker recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Strong Password Checker interview FAQ
Is this really asked at companies like Wix and Flipkart?+
Yes. It appears in the reported interview histories of Devtron, Wix, and Flipkart. The exact frequency varies by team and hiring cycle, but this is a real problem in circulation at those companies, not a theoretical edge case.
What makes this harder than normal string problems?+
You're optimizing across three independent constraints simultaneously, not just one. Most string problems let you fix issues in isolation. Here, an edit that satisfies one rule might partially satisfy another, forcing you to think about interaction effects and prioritization.
Do I need a heap for this?+
Not strictly. Heaps help you efficiently grab the longest repeating sequence when inserting, but you can track it with a counter and iteration. However, knowing heap patterns listed in the topics means the problem setter considered that approach valid.
What's the main greedy trick I'm missing?+
When deleting characters to remove repeats, prioritize sequences with length modulo 3 equal to 1 or 2 first. They give you more payoff per deletion. On insertions, target the longest repeating sequence. That ordering is the core insight.
How does this relate to the other listed topics?+
String handles the password validation logic. Greedy is the actual algorithm for minimizing edits by prioritizing high-impact operations. Heap is an optional optimization for tracking the longest sequences efficiently.
Want the actual problem statement? View "Strong Password Checker" on LeetCode →