Stamping The Sequence
A hard-tier problem at 62% community acceptance, tagged with String, Stack, Greedy. Reported in interviews at Morgan Stanley and 0 others.
Stamping the Sequence is a hard string problem that hits you with a deceptive premise: you have a stamp and need to reverse-engineer which stamps created a target string. Morgan Stanley has asked it. The catch is that you can't just simulate forward. You need to work backwards, peeling off stamped sequences until you're left with nothing. If you blank on the reversal trick during your live OA, StealthCoder solves it invisibly in seconds, no proctor visibility.
Companies that ask "Stamping The Sequence"
Stamping The Sequence 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 engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe core insight is greedy reversal with a stack-like pattern. Forward simulation fails because overlapping stamps create ambiguity. Instead, scan the target string and greedily remove the stamp pattern from right to left, replacing matched stamps with wildcards so they don't interfere with subsequent removals. The trick is knowing when a stamp match is safe to remove without breaking the overall sequence validity. Stack and queue patterns emerge as you track which positions have been stamped. Common failure: trying to simulate the stamping process forward, which gets tangled in overlaps. When you hit this wall on the assessment and the forward approach crumbles, StealthCoder surfaces the backwards-greedy solution instantly.
Pattern tags
You know the problem.
Make sure you actually pass it.
Stamping The Sequence recycles across companies for a reason. It's hard-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 engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Stamping The Sequence interview FAQ
Is this really a hard problem or does the acceptance rate overstate it?+
Acceptance rate is 61.8%, which is misleading for a hard. The problem is genuinely hard because the reversal insight doesn't come naturally. Once you see it, implementation is tractable. Most people struggle on the jump from forward simulation to backward greedy.
How does this differ from typical string manipulation problems?+
Stamping the Sequence combines string matching with greedy strategy and requires inverting your problem perspective. Unlike regex or pattern matching, you're working backwards to prove a sequence is valid, not building it forward.
Will I see this at other companies or is Morgan Stanley unique?+
Morgan Stanley is the only reported company in the data. However, the underlying pattern (greedy reversal, backward validation) appears in other hard interview problems across different sectors. It's not exclusive but not common.
Do I need to know queue and stack details to solve this?+
You'll use stack and queue patterns to track positions and validate sequences, but not as primary data structures. Understanding the greedy removal logic is more critical than queue/stack theory. They're implementation details, not the core insight.
What's the most common way candidates fail this in interviews?+
Trying to simulate stamping forward and getting lost in overlaps. The moment you realize forward doesn't work cleanly, you need to flip to backwards greedy. Hesitation on that pivot is what costs time on the live assessment.
Want the actual problem statement? View "Stamping The Sequence" on LeetCode →