##### Welcome to Subscribe On Youtube

Formatted question description: https://leetcode.ca/all/2210.html

# 2210. Count Hills and Valleys in an Array (Easy)

You are given a **0-indexed** integer array `nums`

. An index `i`

is part of a **hill** in `nums`

if the closest non-equal neighbors of `i`

are smaller than `nums[i]`

. Similarly, an index `i`

is part of a **valley** in `nums`

if the closest non-equal neighbors of `i`

are larger than `nums[i]`

. Adjacent indices `i`

and `j`

are part of the **same** hill or valley if `nums[i] == nums[j]`

.

Note that for an index to be part of a hill or valley, it must have a non-equal neighbor on **both** the left and right of the index.

Return *the number of hills and valleys in *`nums`

.

**Example 1:**

Input:nums = [2,4,1,1,6,5]Output:3Explanation:At index 0: There is no non-equal neighbor of 2 on the left, so index 0 is neither a hill nor a valley. At index 1: The closest non-equal neighbors of 4 are 2 and 1. Since 4 > 2 and 4 > 1, index 1 is a hill. At index 2: The closest non-equal neighbors of 1 are 4 and 6. Since 1 < 4 and 1 < 6, index 2 is a valley. At index 3: The closest non-equal neighbors of 1 are 4 and 6. Since 1 < 4 and 1 < 6, index 3 is a valley, but note that it is part of the same valley as index 2. At index 4: The closest non-equal neighbors of 6 are 1 and 5. Since 6 > 1 and 6 > 5, index 4 is a hill. At index 5: There is no non-equal neighbor of 5 on the right, so index 5 is neither a hill nor a valley. There are 3 hills and valleys so we return 3.

**Example 2:**

Input:nums = [6,6,5,5,4,1]Output:0Explanation:At index 0: There is no non-equal neighbor of 6 on the left, so index 0 is neither a hill nor a valley. At index 1: There is no non-equal neighbor of 6 on the left, so index 1 is neither a hill nor a valley. At index 2: The closest non-equal neighbors of 5 are 6 and 4. Since 5 < 6 and 5 > 4, index 2 is neither a hill nor a valley. At index 3: The closest non-equal neighbors of 5 are 6 and 4. Since 5 < 6 and 5 > 4, index 3 is neither a hill nor a valley. At index 4: The closest non-equal neighbors of 4 are 5 and 1. Since 4 < 5 and 4 > 1, index 4 is neither a hill nor a valley. At index 5: There is no non-equal neighbor of 1 on the right, so index 5 is neither a hill nor a valley. There are 0 hills and valleys so we return 0.

**Constraints:**

`3 <= nums.length <= 100`

`1 <= nums[i] <= 100`

**Similar Questions**:

- Find Peak Element (Medium)
- Monotonic Array (Easy)
- Minimum Subsequence in Non-Increasing Order (Easy)

## Solution 1. Brute Force

Since we skip consecutive equal numbers, and for each number we stop at its previous and next non-equal numbers, this algorithm takes `O(N)`

time.

```
// OJ: https://leetcode.com/problems/count-hills-and-valleys-in-an-array/
// Time: O(N)
// Space: O(1)
class Solution {
public:
int countHillValley(vector<int>& A) {
int N = A.size(), ans = 0;
for (int i = 1; i < N; ++i) {
if (A[i] == A[i - 1]) continue;
int j = i, k = i;
while (j >= 0 && A[j] == A[i]) --j;
while (k < N && A[k] == A[i]) ++k;
if (j >= 0 && k < N && ((A[j] > A[i] && A[k] > A[i]) || (A[j] < A[i] && A[k] < A[i]))) ++ans;
}
return ans;
}
};
```