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2420. Find All Good Indices 👍

Problem

You are given a 0-indexed integer array nums of size n and a positive integer k.

We call an index i in the range k <= i < n - k good if the following conditions are satisfied:

  • The k elements that are just before the index i are in non-increasing order.
  • The k elements that are just after the index i are in non-decreasing order.

Return an array of all good indices sorted in increasing order.

 

Example 1:

Input: nums = [2,1,1,1,3,4,1], k = 2
Output: [2,3]
Explanation: There are two good indices in the array:
- Index 2. The subarray [2,1] is in non-increasing order, and the subarray [1,3] is in non-decreasing order.
- Index 3. The subarray [1,1] is in non-increasing order, and the subarray [3,4] is in non-decreasing order.
Note that the index 4 is not good because [4,1] is not non-decreasing.

Example 2:

Input: nums = [2,1,1,2], k = 2
Output: []
Explanation: There are no good indices in this array.

 

Constraints:

  • n == nums.length
  • 3 <= n <= 105
  • 1 <= nums[i] <= 106
  • 1 <= k <= n / 2