[LeetCode Sync] Runtime - 54 ms (63.14%), Memory - 21.4 MB (99.40%)

Author: NinePiece2

Solutions/3374-count-alternating-subarrays/README.md

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+<p>You are given a <span data-keyword="binary-array">binary array</span> <code>nums</code>.</p>
+
+<p>We call a <span data-keyword="subarray-nonempty">subarray</span> <strong>alternating</strong> if <strong>no</strong> two <strong>adjacent</strong> elements in the subarray have the <strong>same</strong> value.</p>
+
+<p>Return <em>the number of alternating subarrays in </em><code>nums</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [0,1,1,1]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">5</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<p>The following subarrays are alternating: <code>[0]</code>, <code>[1]</code>, <code>[1]</code>, <code>[1]</code>, and <code>[0,1]</code>.</p>
+</div>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [1,0,1,0]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">10</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<p>Every subarray of the array is alternating. There are 10 possible subarrays that we can choose.</p>
+</div>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>nums[i]</code> is either <code>0</code> or <code>1</code>.</li>
+</ul>

Solutions/3374-count-alternating-subarrays/solution.py

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+class Solution:
+    def countAlternatingSubarrays(self, nums: List[int]) -> int:
+        result = 1
+        sum_val = 1
+        for val1, val2 in pairwise(nums):
+            sum_val = sum_val + 1 if val1 != val2 else 1
+            result += sum_val
+        
+        return result