Max Chunks To Make Sorted II

HardStackmonotonic 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

You are given an integer array arr, which may contain duplicates. Split it into contiguous **chunks**, sort each chunk on its own, and concatenate the chunks back in their original order. The split is valid if the result equals arr sorted in non-decreasing order. Return the **largest** number of chunks in a valid split. Aim for O(n) time with a stack, or O(n log n) by comparing against the sorted array.

Examples

Input: arr = [5,4,3,2,1]
Output: 1
Any cut leaves a larger number in front of a smaller one in a later chunk, so the whole array must be one chunk.
Input: arr = [2,1,3,4,4]
Output: 4
Split as [2,1], [3], [4], [4].

Constraints

  • 1 <= arr.length <= 2000
  • 0 <= arr[i] <= 10^8

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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