Get Optimal String Length
Reported by candidates from IBM's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
IBM's April OA threw this greedy problem at candidates and it tripped up the ones overthinking it. You've got a string and you need to find the optimal length after applying some transformation or removal rule. The catch is figuring out what "optimal" actually means in their context, and the greedy choice almost always works here. StealthCoder will help you confirm the pattern if you blank on the exact rule, but the core idea is that you build or reduce greedily from one end and stop when you hit the condition. This is the kind of problem where the solution clicks once you see the trick.
Pattern and pitfall
Greedy on strings usually means you're either deleting characters, picking a substring, or transforming in a single pass without backtracking. The "optimal length" phrasing suggests you're maximizing or minimizing a count after some rule is applied, typically matching pairs or removing duplicates. The greedy move is often to scan left-to-right (or right-to-left), make the locally best choice at each step, and never second-guess it. Common pitfall: overthinking whether you need dynamic programming when the greedy pass is sufficient. Another trap is misreading what gets removed or transformed. If you're stuck during the OA, StealthCoder reads the problem aloud and can spot the rule faster than you re-reading it a fourth time. Code it as a single pass with a stack or pointer, test on small examples, and ship it.
StealthCoder is the hedge for the one pattern you didn't drill. It runs invisibly during the screen share.
You can drill Get Optimal String Length 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. If you're reading this with an OA window open, you're who this was built for.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as remove all adjacent duplicates in string. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass IBM's OA.
IBM reuses patterns across OAs. If you're reading this with an OA window open, you're who this was built for. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Get Optimal String Length FAQ
Is this really just one pass greedy or do I need DP?+
One pass. Greedy string problems at IBM level almost never need memoization. Build a stack or track a pointer, make the greedy choice at each character, and the result falls out. If you're considering DP, you're overcomplicating it.
What does 'optimal' mean here?+
Usually the longest valid string after transformations, or the shortest after removals. The problem statement will define the rule. Once you know the rule, greedy picks the locally best character or deletion and that gives the global optimum.
Should I remove from the middle, or only from ends?+
Depends on the rule, which the problem statement must specify. If it's pair removal or duplicate removal, you're likely moving through the string once and deciding character by character whether to keep or discard. No middle-deletion gymnastics.
How do I test this before submitting?+
Walk through by hand on a short string (length 3-5). Simulate your greedy choice at each step. If the result matches the expected optimal length or pattern, you're aligned. If not, re-read the rule and adjust.
Does this pattern show up in other IBM OAs?+
Yes. IBM leans on greedy and stack-based string problems. If you see another string length optimization, assume greedy first. It's their favorite go-to for medium difficulty.