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Author: jimit105

2316-count-hills-and-valleys-in-an-array/README.md

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+<p>You are given a <strong>0-indexed</strong> integer array <code>nums</code>. An index <code>i</code> is part of a <strong>hill</strong> in <code>nums</code> if the closest non-equal neighbors of <code>i</code> are smaller than <code>nums[i]</code>. Similarly, an index <code>i</code> is part of a <strong>valley</strong> in <code>nums</code> if the closest non-equal neighbors of <code>i</code> are larger than <code>nums[i]</code>. Adjacent indices <code>i</code> and <code>j</code> are part of the <strong>same</strong> hill or valley if <code>nums[i] == nums[j]</code>.</p>
+
+<p>Note that for an index to be part of a hill or valley, it must have a non-equal neighbor on <strong>both</strong> the left and right of the index.</p>
+
+<p>Return <i>the number of hills and valleys in </i><code>nums</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [2,4,1,1,6,5]
+<strong>Output:</strong> 3
+<strong>Explanation:</strong>
+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 &gt; 2 and 4 &gt; 1, index 1 is a hill. 
+At index 2: The closest non-equal neighbors of 1 are 4 and 6. Since 1 &lt; 4 and 1 &lt; 6, index 2 is a valley.
+At index 3: The closest non-equal neighbors of 1 are 4 and 6. Since 1 &lt; 4 and 1 &lt; 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 &gt; 1 and 6 &gt; 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.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [6,6,5,5,4,1]
+<strong>Output:</strong> 0
+<strong>Explanation:</strong>
+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 &lt; 6 and 5 &gt; 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 &lt; 6 and 5 &gt; 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 &lt; 5 and 4 &gt; 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.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>3 &lt;= nums.length &lt;= 100</code></li>
+	<li><code>1 &lt;= nums[i] &lt;= 100</code></li>
+</ul>

2316-count-hills-and-valleys-in-an-array/solution.py

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+# Time: O(n)
+# Space: O(n)
+
+class Solution:
+    def countHillValley(self, nums: List[int]) -> int:
+        # Remove consecutive duplicates
+        filtered = []
+        for num in nums:
+            if not filtered or filtered[-1] != num:
+                filtered.append(num)
+        
+        count = 0
+        for i in range(1, len(filtered) - 1):
+            # Hill condition
+            if filtered[i] > filtered[i - 1] and filtered[i] > filtered[i + 1]:
+                count += 1
+            # Valley condition
+            elif filtered[i] < filtered[i - 1] and filtered[i] < filtered[i + 1]:
+                count += 1
+
+        return count
+