An element strictly greater than both neighbors; the first and last elements can never be peaks.
[1,4,3,8,5] → peaks at indices [1,3]. (LeetCode 2951)
class Solution { public List<Integer> findPeaks(int[] mountain) { int n = mountain.length; List<Integer> result = new ArrayList<>();
for(int i = 0; i < n; i++){ if(i == 0 || i == n-1){ continue; } if(mountain[i] > mountain[i-1] && mountain[i] > mountain[i+1]){ result.add(i); } } return result; }}