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Classic problem #2951EasyArrayEnumeration

Find the Peaks

Real-world version: Ridge Points Along the Profile
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The statement here is our own: the same inputs, outputs and technique.

A survey profile is given as mountain, where mountain[i] is the height at station i.

A station is a ridge point when it is strictly higher than the station on each side of it. The first and last stations are never ridge points, since each has only one neighbour.

Return the ridge point stations in increasing order.

Examples

Example 1

Input
mountain = [2, 5, 3, 6, 4]
Output
[1, 3]

Station 1 stands at 5 above the 2 and the 3 beside it, and station 3 stands at 6 above the 3 and the 4 beside it.

Example 2

Input
mountain = [1, 3, 3, 1]
Output
[]

Stations 1 and 2 are both at height 3, so neither stands strictly above both of its neighbours.

Example 3

Input
mountain = [1, 2, 3]
Output
[]

The only station with a neighbour on each side is station 1, and it stands below station 2.

Constraints

  • 3 <= mountain.length <= 100
  • 1 <= mountain[i] <= 100

The signature

The editor starts with this. It matches the parent problem's shape, so a solution that works here works on a standard judge unchanged.

Python
def ridge_points(mountain: list[int]) -> list[int]:
Java
public List<Integer> ridgePoints(int[] mountain)

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