Min Operations to Make Array Equal
Reported by candidates from DE Shaw's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
DE Shaw's March OA included a problem on making an array equal with minimum operations. You're staring at an array and need to figure out the cheapest way to transform it into a uniform state. The trap is overthinking which element to equalize toward. This is a classic optimization problem where the answer lives in the math, not the brute force. StealthCoder can feed you the pattern instantly if you blank on the approach.
Pattern and pitfall
The key insight: you're not trying every possible target value. The optimal target is the median of the array. Any element not equal to the median needs one operation to change. Why median? Because it minimizes the sum of absolute differences. Count how many elements differ from the median, and that's your answer. The common miss is treating this as a graph or greedy problem when it's pure math. If the problem allows any target value, calculate the median once, iterate the array once, and count mismatches. That's O(n) and clean. StealthCoder will show you this pattern the moment you see the problem statement in the OA interface.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Min Operations to Make Array Equal cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Made for the candidate who got the OA invite this morning and has 72 hours, not six months.
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This OA pattern shows up on LeetCode as minimum moves to equal array elements. If you have time before the OA, drill that.
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Make sure you actually pass DE Shaw's OA.
DE Shaw reuses patterns across OAs. Made for the candidate who got the OA invite this morning and has 72 hours, not six months. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Min Operations to Make Array Equal FAQ
Do I need to actually change the array, or just count operations?+
Just count. You're returning the minimum number of operations required, not the transformed array. One operation per element that doesn't match the median. Don't waste time simulating changes.
What if the array has an even number of elements?+
Any value between the two middle elements (inclusive) minimizes operations. Typically, pick the lower or upper median. Both give the same operation count. The math holds either way.
Is this really just a median problem?+
Yes. Median minimizes absolute deviations. If you're counting operations to make all elements equal, the target must be the median. This is a well-known principle in statistics and algorithm design.
What if all elements are already equal?+
Zero operations. The median equals every element, so no mismatches. Edge case that often trips up candidates who don't handle it explicitly.
How do I verify I got the median right?+
Sort the array, grab the middle element(s). If odd length, it's index n/2. If even, either middle element works. Then iterate the original array and count elements not equal to that median value.