Jumped straight to brute force in my head and had to stop myself.
Clarify the problem constraints (e.g., array size, whether circular, handling duplicates) and then propose an O(n) solution using a monotonic stack. Explain the algorithm step-by-step, analyze time and space complexity, and discuss potential optimizations or variations.
Pro tip: Mention that the monotonic stack approach is optimal and can be adapted for circular arrays or to find previous greater elements. Also, relate it to ML engineering tasks like feature engineering or sequence processing to show practical relevance.
Ask about input size, whether the array is circular, how to handle duplicates, and expected output format (e.g., return array of next greater or -1 if none).
Describe the monotonic stack approach: iterate through the array, maintain a stack of indices with decreasing values, and for each element, pop and assign next greater until stack top is greater.
Trace the algorithm on a small example (e.g., [2,1,2,4,3]) to demonstrate correctness and how the stack evolves.
State that each element is pushed and popped at most once, giving O(n) time and O(n) space in the worst case.
Mention variations like circular arrays (iterate twice), previous greater element, or using the same pattern for other problems (e.g., daily temperatures).
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