Monotonic Array

EasyArrays & Hashingsimulation

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

An array is **monotonic** if it never goes down (every nums[i] <= nums[i+1]) or never goes up (every nums[i] >= nums[i+1]). Equal neighbours are allowed in both cases. Given an integer array nums, return true if it is monotonic and false otherwise. A single-element array is monotonic. Solve it in one pass with O(1) extra space.

Examples

Input: nums = [1,2,2,3]
Output: true
Values never decrease.
Input: nums = [6,5,4,4]
Output: true
Values never increase.
Input: nums = [1,3,2]
Output: false
It goes up from 1 to 3 and then down to 2.

Constraints

  • 1 <= nums.length <= 10^5
  • -10^5 <= nums[i] <= 10^5
  • Equal adjacent values do not break monotonicity.

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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