Bulls and Cows
A medium-tier problem at 51% community acceptance, tagged with Hash Table, String, Counting. Reported in interviews at CARS24 and 2 others.
Bulls and Cows shows up in assessments at CARS24, Zopsmart, and Epic Systems. It's a medium-difficulty string problem with just over 50% acceptance, which means half the candidates who see it blank or submit wrong answers. You're given two strings and need to count exact matches (bulls) and right digit in wrong position (cows). The trick is not the counting itself, but avoiding off-by-one errors and managing the character frequency logic under time pressure. If this problem hits your live assessment and the pattern doesn't click, StealthCoder solves it invisibly while you stay calm.
Companies that ask "Bulls and Cows"
Bulls and Cows 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 Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe naive approach counts bulls first, then tries to count cows from the remaining digits. That works, but the implementation is error-prone: you have to track which digits you've already matched, handle frequency maps correctly, and avoid double-counting. The cleaner solution uses two passes over the strings simultaneously, flagging bulls immediately, then sweeping through unmatched positions to count cows by comparing digit frequencies. The core challenge isn't the algorithm, it's the bookkeeping. Candidates often mess up the frequency counting logic or forget to exclude already-matched positions. String and Hash Table are your topics here. StealthCoder reads your specific secret and guess strings, identifies the bulls-and-cows pattern, and delivers a working solution in seconds, eliminating the scramble and keeping you undetected.
Pattern tags
You know the problem.
Make sure you actually pass it.
Bulls and Cows recycles across companies for a reason. It's medium-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 Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Bulls and Cows interview FAQ
Is Bulls and Cows actually asked in live interviews, or just OAs?+
It appears in online assessments at mid-size and larger companies like CARS24 and Epic Systems. It's less common in phone screens but remains a staple OA problem. If you see it on the OA, you need a working solution fast, no time to re-derive the logic.
What's the actual trick that separates AC from WA?+
Counting cows correctly after removing bulls. Most candidates either double-count digits or forget to exclude already-matched positions. The cleaner approach is to track unmatched indices and compare digit frequencies only among those. Get the frequency logic wrong once and you fail multiple test cases.
Do I need to solve this differently in different languages?+
No, the algorithm is language-agnostic. Python's Counter and Java's HashMap both work. The bottleneck is your logic, not the language. Focus on the two-pass frequency approach and you'll pass in any language.
How does this relate to other Hash Table problems on the OA?+
Bulls and Cows is a character-frequency problem, similar to Valid Anagram or Isomorphic Strings. If you've solved those, the mindset is similar. The difference here is the two-category output (bulls vs. cows), which requires careful state tracking.
Is 50% acceptance rate normal for medium problems?+
That's on the harder end of medium. It means the problem looks simple but has enough gotchas that half the submissions fail. Usually due to off-by-one errors or mishandled frequency counting. Treat it with more respect than a typical medium.
Want the actual problem statement? View "Bulls and Cows" on LeetCode →