1574. Shortest Subarray to be Removed to Make Array Sorted

Description

Given an integer array arr, remove a subarray (can be empty) from arr such that the remaining elements in arr are non-decreasing.

Return the length of the shortest subarray to remove.

A subarray is a contiguous subsequence of the array.

Example 1:

Input: arr = [1,2,3,10,4,2,3,5]
Output: 3
Explanation: The shortest subarray we can remove is [10,4,2] of length 3. The remaining elements after that will be [1,2,3,3,5] which are sorted.
Another correct solution is to remove the subarray [3,10,4].

Example 2:

Input: arr = [5,4,3,2,1]
Output: 4
Explanation: Since the array is strictly decreasing, we can only keep a single element. Therefore we need to remove a subarray of length 4, either [5,4,3,2] or [4,3,2,1].

Example 3:

Input: arr = [1,2,3]
Output: 0
Explanation: The array is already non-decreasing. We do not need to remove any elements.

Constraints:

1 <= arr.length <= 10⁵
0 <= arr[i] <= 10⁹

Solution

shortest-subarray-to-be-removed-to-make-array-sorted.py

class Solution:
    def findLengthOfShortestSubarray(self, arr: List[int]) -> int:
        n = len(arr)
        left = 0

        while left+1 < n and arr[left] <= arr[left+1]: left += 1

        if left + 1 == n: return 0

        right = n-1

        while left < right and arr[right] >= arr[right-1]: right -= 1

        res = min(n - left - 1, right)
        i = 0
        j = right
        while i <= left and j < n:
            if arr[j] >= arr[i]:
                res = min(res, j - i - 1)
                i += 1
            else:
                j += 1


        return res

shortest-subarray-to-be-removed-to-make-array-sorted.cpp

class Solution {
public:
    int findLengthOfShortestSubarray(vector<int>& arr) {
        int n = arr.size();
        int left = 0;
        while (left+1 < n && arr[left+1] >= arr[left]) left++;
        if (left+1 == n) return 0;

        int right = n-1;
        while (right > left && arr[right-1] <= arr[right]) right--;

        int res = min(n - left - 1, right);
        int i = 0, j = right;

        while (i <= left && j < n){
            if (arr[j] >= arr[i]){
                res = min(res, j - i - 1);
                i++;
            }else{
                j++;
            }
        }

        return res;
    }
};