動機

基本上看到seg與要順序都可以猜用Monotonic Stack 這裡可以直接抄768用

Problem

You are given an integer array arr.

We split arr into some number of chunks (i.e., partitions), and individually sort each chunk. After concatenating them, the result should equal the sorted array.

Return the largest number of chunks we can make to sort the array.

 

Example 1:

Input: arr = [5,4,3,2,1]Output: 1Explanation:Splitting into two or more chunks will not return the required result.For example, splitting into [5, 4], [3, 2, 1] will result in [4, 5, 1, 2, 3], which isn't sorted.

Example 2:

Input: arr = [2,1,3,4,4]Output: 4Explanation:We can split into two chunks, such as [2, 1], [3, 4, 4].However, splitting into [2, 1], [3], [4], [4] is the highest number of chunks possible.

 

Constraints:

  • 1 <= arr.length <= 2000
  • 0 <= arr[i] <= 108

Sol

class Solution:
    def maxChunksToSorted(self, arr: List[int]) -> int:
        stk = []
        for n in arr:
            maxN = n
            while stk and stk[-1] > n:
                maxN = max(maxN, stk.pop())
            stk += maxN,
        return len(stk)