Sync LeetCode submission Runtime - 1 ms (94.90%), Memory - 17.8 MB (74.08%)

Author: jimit105

3685-count-subarrays-of-length-three-with-a-condition/README.md

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+<p>Given an integer array <code>nums</code>, return the number of <span data-keyword="subarray-nonempty">subarrays</span> of length 3 such that the sum of the first and third numbers equals <em>exactly</em> half of the second number.</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 = [1,2,1,4,1]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">1</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<p>Only the subarray <code>[1,4,1]</code> contains exactly 3 elements where the sum of the first and third numbers equals half the middle number.</p>
+</div>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [1,1,1]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">0</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<p><code>[1,1,1]</code> is the only subarray of length 3. However, its first and third numbers do not add to half the middle number.</p>
+</div>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>3 &lt;= nums.length &lt;= 100</code></li>
+	<li><code><font face="monospace">-100 &lt;= nums[i] &lt;= 100</font></code></li>
+</ul>

3685-count-subarrays-of-length-three-with-a-condition/solution.py

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+# Approach: One Time Traversal
+
+# Time: O(n)
+# Space: O(1)
+
+class Solution:
+    def countSubarrays(self, nums: List[int]) -> int:
+        ans = 0
+
+        for i in range(1, len(nums) - 1):
+            if nums[i] == (nums[i - 1] + nums[i + 1]) * 2:
+                ans += 1
+
+        return ans
+
+