Minimum Number of Operations to Sort a Binary Tree by Level
A medium-tier problem at 74% community acceptance, tagged with Tree, Breadth-First Search, Binary Tree. Reported in interviews at Guidewire and 0 others.
You're doing a Guidewire assessment and hit a tree problem that asks you to sort nodes by level. Your instinct is probably to build a level-order traversal, grab the values, sort them, then count swaps. That works, but the catch is figuring out what "minimum operations" actually means and how to count them correctly without overthinking it. The problem looks straightforward (70% pass rate), but the gap between "I see what's happening" and "I can code the swap count right" is where people lose time.
Companies that ask "Minimum Number of Operations to Sort a Binary Tree by Level"
Minimum Number of Operations to Sort a Binary Tree by Level 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. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoderThe trap is thinking you need to simulate the swaps or track which nodes move where. What you actually need: BFS to collect values at each level, sort those values, then count how many positions are wrong. The minimum swaps to sort an array is the number of elements not in their final sorted position, or you can think of it as the array size minus the longest increasing subsequence of indices. Most candidates either implement a full permutation cycle counter (overcomplicating it) or miscalculate what "sorted" means in the context of each level independently. If you blank on the counting logic during the live OA, StealthCoder surfaces the working solution in seconds so you can keep moving and not burn 20 minutes debugging swap logic.
Pattern tags
You know the problem.
Make sure you actually pass it.
Minimum Number of Operations to Sort a Binary Tree by Level 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. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Number of Operations to Sort a Binary Tree by Level interview FAQ
Is this problem actually asked at interviews?+
Guidewire has reported it. It's a MEDIUM rated tree+BFS problem with a 74% acceptance rate, so it's positioned as accessible but not trivial. If you're interviewing there, it's a realistic candidate.
What's the actual trick?+
You need to isolate each level, sort the values at that level, and count mismatches. The minimum swaps is not about simulating the swaps; it's about counting how many elements are in wrong positions compared to the sorted array. Most people overcomplicate the counting.
Can I just do a level-order traversal and sort?+
Yes. Do BFS to extract values level by level, sort each level's values, then compare against the original. Count positions where original and sorted differ. That's your answer. Don't overthink permutation cycles unless you're asked to optimize space.
Is this really a MEDIUM or does it feel harder?+
The 74% pass rate backs up the MEDIUM label. The BFS part is basic. The swap-count logic is where people stumble. If you've seen this pattern before, it's quick. Cold, it can eat 20 minutes of your OA time.
Does this relate to other tree interview questions?+
It mixes Breadth-First Search with a sorting/counting problem. If you're solid on BFS and can count array inversions or mismatches, you're 80% there. The tree part is mostly scaffolding; the real work is the level-by-level comparison.
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