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3285. Find Indices of Stable Mountains
Description
There are n
mountains in a row, and each mountain has a height. You are given an integer array height
where height[i]
represents the height of mountain i
, and an integer threshold
.
A mountain is called stable if the mountain just before it (if it exists) has a height strictly greater than threshold
. Note that mountain 0 is not stable.
Return an array containing the indices of all stable mountains in any order.
Example 1:
Input: height = [1,2,3,4,5], threshold = 2
Output: [3,4]
Explanation:
 Mountain 3 is stable because
height[2] == 3
is greater thanthreshold == 2
.  Mountain 4 is stable because
height[3] == 4
is greater thanthreshold == 2
.
Example 2:
Input: height = [10,1,10,1,10], threshold = 3
Output: [1,3]
Example 3:
Input: height = [10,1,10,1,10], threshold = 10
Output: []
Constraints:
2 <= n == height.length <= 100
1 <= height[i] <= 100
1 <= threshold <= 100
Solutions
Solution 1: Traversal
We directly traverse the mountains starting from index $1$. If the height of the mountain to its left is greater than $threshold$, we add its index to the result array.
After the traversal, we return the result array.
The time complexity is $O(n)$, where $n$ is the length of the array $\textit{height}$. Ignoring the space consumption of the result array, the space complexity is $O(1)$.

class Solution { public List<Integer> stableMountains(int[] height, int threshold) { List<Integer> ans = new ArrayList<>(); for (int i = 1; i < height.length; ++i) { if (height[i  1] > threshold) { ans.add(i); } } return ans; } }

class Solution { public: vector<int> stableMountains(vector<int>& height, int threshold) { vector<int> ans; for (int i = 1; i < height.size(); ++i) { if (height[i  1] > threshold) { ans.push_back(i); } } return ans; } };

class Solution: def stableMountains(self, height: List[int], threshold: int) > List[int]: return [i for i in range(1, len(height)) if height[i  1] > threshold]

func stableMountains(height []int, threshold int) (ans []int) { for i := 1; i < len(height); i++ { if height[i1] > threshold { ans = append(ans, i) } } return }

function stableMountains(height: number[], threshold: number): number[] { const ans: number[] = []; for (let i = 1; i < height.length; ++i) { if (height[i  1] > threshold) { ans.push(i); } } return ans; }