Wiggle Subsequence

MediumGreedygreedy

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

A sequence is a **wiggle sequence** if the differences between consecutive elements strictly alternate between positive and negative. A sequence with one element, or with two different elements, counts as a wiggle sequence; a zero difference is never allowed. Given an integer array nums, return the length of its longest subsequence (keeping the original order, possibly skipping elements) that is a wiggle sequence. Aim for O(n) time.

Examples

Input: nums = [1,7,4,9,2,5]
Output: 6
The whole array wiggles: +6, -3, +5, -7, +3.
Input: nums = [1,17,5,10,13,15,10,5,16,8]
Output: 7
One longest choice is [1,17,10,13,10,16,8].
Input: nums = [1,2,3,4,5,6,7,8,9]
Output: 2
Only one rise can be kept, e.g. [1,9].

Constraints

  • 1 <= nums.length <= 1000
  • 0 <= nums[i] <= 1000

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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