Find Lexicographically Smallest String
Reported by candidates from Amazon's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Amazon's December OA is asking you to find the lexicographically smallest string, a classic string manipulation problem that sounds simpler than it is. You're likely being given a string and a set of operations, and you need to apply them in the right order to minimize the result. This isn't about brute force. It's about understanding which operations to apply, when, and how many times. StealthCoder will catch the pattern in real time if you freeze on the logic.
Pattern and pitfall
The trick here is recognizing that you're not searching through all permutations. Instead, you're greedily applying allowed operations in a way that reduces characters or reorders them lexicographically. The pattern is usually greedy with a twist: some operations are worth repeating, others aren't. You'll likely iterate through the string from left to right, replacing or swapping characters to make each position as small as possible. The pitfall is not recognizing that certain operations enable others, creating a dependency chain. Common approach: use a queue or greedy simulation to track which operations to apply. StealthCoder becomes your safety net if you blank on whether to loop until no changes occur or apply operations once.
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You can drill Find Lexicographically Smallest String 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.
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Find Lexicographically Smallest String FAQ
What does 'lexicographically smallest' mean here?+
It means the string that comes first alphabetically. 'a' is smaller than 'b'. When comparing strings, you compare character by character from left to right. So 'abc' is smaller than 'abd'. Your goal is to rearrange or modify the string so it ranks as low as possible in dictionary order.
Is this a greedy problem?+
Very likely. Greedy usually works when you want lexicographically smallest: prioritize making the leftmost character as small as possible, then the next, and so on. But check if operations interact. Sometimes you need to apply one operation multiple times before moving to the next, or vice versa.
Do I need dynamic programming?+
Probably not. DP is overkill for lexicographic minimization. This is more simulation or greedy with a while loop. Apply operations until no more changes happen, or apply each operation greedily in the correct order. No need for memoization or state tracking.
What if the operations aren't specified clearly?+
Read the examples. The examples will show you what operations are allowed. Usually it's swaps, replacements, or transformations of adjacent characters. Trace through an example by hand to see the pattern. That's your contract with the problem.
How do I prepare in 48 hours?+
Understand the operations, trace one example by hand, code a greedy or simulation approach, and test on the example. Focus on correctness over optimization. Edge cases: single character, already sorted, no valid operations. You don't need to memorize patterns, you need to read carefully and code clearly.