Find the Most Competitive Subsequence

MediumStackmonotonic stack

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given an integer array nums and a positive integer k <= nums.length, return the subsequence of nums of length exactly k that is **lexicographically smallest** (the "most competitive"). Subsequences keep the original relative order. Comparing two equal-length sequences, the smaller one is the one with the smaller value at the first index where they differ. Aim for O(n) time.

Examples

Input: nums = [3,5,2,6], k = 2
Output: [2,6]
Of all length-2 subsequences ([3,5], [3,2], [3,6], [5,2], [5,6], [2,6]), [2,6] is smallest.
Input: nums = [2,4,3,3,5,4,9,6], k = 4
Output: [2,3,3,4]
Pick 2, both 3s, and the 4 at index 5.

Constraints

  • 1 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9
  • 1 <= k <= nums.length

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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