- Difficulty: Medium
- Tags: LeetCode, Medium, Array, Dynamic Programming, Prefix Sum, leetcode-2420, O(n)
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 indexi
are in non-increasing order. - The
k
elements that are just after the indexi
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