769. Max Chunks To Make Sorted

769. Max Chunks To Make Sorted

Medium

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You are given an integer array arr of length n that represents a permutation of the integers in the range [0, n - 1].

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 = [4,3,2,1,0]
Output: 1
Explanation:
Splitting into two or more chunks will not return the required result.
For example, splitting into [4, 3], [2, 1, 0] will result in [3, 4, 0, 1, 2], which isn't sorted.

Example 2:

Input: arr = [1,0,2,3,4]
Output: 4
Explanation:
We can split into two chunks, such as [1, 0], [2, 3, 4].
However, splitting into [1, 0], [2], [3], [4] is the highest number of chunks possible.

Constraints:

• n == arr.length
• 1 <= n <= 10
• 0 <= arr[i] < n
• All the elements of arr are unique.

Refer to other people's questions ：

class Solution:
    def maxChunksToSorted(self, arr: List[int]) -> int:
        """
        assert Solution().maxChunksToSorted([1, 4, 0, 2, 3, 5]) == 2
        assert Solution().maxChunksToSorted([0, 2, 1]) == 2
        assert Solution().maxChunksToSorted([1, 2, 0, 3]) == 2
        assert Solution().maxChunksToSorted([0, 1, 2]) == 3
        assert Solution().maxChunksToSorted([0, 1]) == 2
        assert Solution().maxChunksToSorted([4, 3, 2, 1, 0]) == 1
        assert Solution().maxChunksToSorted([1, 0, 2, 3, 4]) == 4
        assert Solution().maxChunksToSorted([0]) == 1

         Can't ！
         Refer to other people's ideas for solving problems ： Traverse from left to right , At the same time, record the current maximum value , Whenever the current maximum value is equal to the array position , We can split again .
         Because when this happens , There is no smaller number on the right than on the left , No need to reorder .
         Time complexity ：O(n)  Spatial complexity ：O(1)
        """
        cnt, maxNum = 0, 0
        for i in range(len(arr)):
            maxNum = max(maxNum, arr[i])
            if maxNum == i:
                cnt += 1
        return cnt