Min Cost
Reported by candidates from IBM's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
IBM asked this in December 2024, and it's a greedy problem disguised as an optimization puzzle. You've got limited resources and need to minimize cost. The trap is trying to use dynamic programming or brute force when a single greedy choice at each step wins. StealthCoder can spot the greedy invariant in seconds if you freeze mid-problem, but the pattern itself is teachable in 90 seconds. Know when to pick the cheapest option now versus holding out for later.
Pattern and pitfall
Min Cost is fundamentally about making locally optimal choices that compound into a global minimum. The greedy approach works when each decision doesn't invalidate future options. Common mistake: overthinking dependencies between choices. You'll be tempted to simulate all states or use DP, but greedy problems reward you for recognizing that a simple rule (always pick the minimum available cost, or always pair the smallest elements, or always consume the cheapest resource first) is provably optimal. The trick is proving to yourself (and the interviewer) why greedy doesn't fail. StealthCoder is your safety net if the greedy property isn't obvious on first read; it'll highlight the pattern so you don't waste 20 minutes on a DP solution that times out.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Min Cost 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. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play.
Get StealthCoderRelated leaked OAs
You've seen the question.
Make sure you actually pass IBM's OA.
IBM reuses patterns across OAs. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Min Cost FAQ
Is this a variation of Huffman coding or task scheduling?+
Without the full problem text, it's hard to say, but greedy problems at IBM often involve pairing elements (like Huffman) or assigning resources in order of cost. If you're building something iteratively and always picking the cheapest next step, that's the signal. Task scheduling and similar problems follow that pattern.
How do I prove greedy works in 2 minutes?+
Show that swapping any two choices increases (or keeps the same) total cost. If the greedy choice is always locally optimal and swapping it never helps globally, you're done. Keep the proof informal in the OA; the code matters more than a rigorous proof.
What if greedy fails on my test case?+
Reread the problem. You may have misunderstood a constraint (like order matters, or elements can't be reused). If you're sure greedy should work, trace through the logic step by step. A single counterexample kills greedy; you'll need DP or backtracking instead.
Should I implement a priority queue or sorting?+
If you're picking the minimum cost multiple times, a min-heap or sort is usually faster than repeated linear scans. If you only pick once or twice, sort and iterate. Profile in your head based on the constraints.
Is this problem still asked after December 2024?+
IBM cycles through similar greedy patterns regularly. Understanding the Min Cost variant from this report teaches you the shape of the problem. If you see any OA ask you to minimize cost by making sequential choices, apply greedy thinking first.