#3392: Count Subarrays of Length Three With a Condition; solution & tests

Author: vetalapo

c-sharp/Problems/sliding-window/CountSubarraysOfLengthThreeWithACondition.cs

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+/**
+ * 3392
+ * Count Subarrays of Length Three With a Condition
+ **
+ * Given an integer array nums,
+ * return the number of subarrays of length 3
+ * such that the sum of the first and third numbers
+ * equals exactly half of the second number.
+ *
+ * Example 1:
+ *   Input: nums = [1,2,1,4,1]
+ *   Output: 1
+ *   Explanation:
+ *     Only the subarray [1,4,1] contains exactly 3 elements
+ *     where the sum of the first and third numbers equals half the middle number.
+ *
+ * Example 2:
+ *   Input: nums = [1,1,1]
+ *   Output: 0
+ *   Explanation:
+ *     [1,1,1] is the only subarray of length 3.
+ *     However,
+ *     its first and third numbers do not add to half the middle number.
+ *
+ * Constraints:
+ *   • 3 <= nums.length <= 100
+ *   • -100 <= nums[i] <= 100
+ *
+ * Hint 1:
+ *   The constraints are small. Consider checking every subarray.
+ **
+ * https://leetcode.com/problems/count-subarrays-of-length-three-with-a-condition/
+***/
+
+namespace Problems;
+
+public class CountSubarraysOfLengthThreeWithACondition
+{
+    public int CountSubarrays( int[] nums )
+    {
+        int count = 0;
+
+        for ( int i = 2; i < nums.Length; i++ )
+        {
+            if ( ( nums[i] + nums[i - 2] ) * 2 == nums[i - 1] )
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
+}

c-sharp/Tests/sliding-window/CountSubarraysOfLengthThreeWithAConditionTests.cs

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+using NUnit.Framework;
+
+using Problems;
+
+public class CountSubarraysOfLengthThreeWithAConditionTests
+{
+    [TestCase( new int[] { 1, 2, 1, 4, 1 }, ExpectedResult = 1 )]
+    [TestCase( new int[] { 1, 1, 1 }, ExpectedResult = 0 )]
+    [TestCase( new int[] { 0, -4, -4 }, ExpectedResult = 0 )]
+    [TestCase( new int[] { -1, -4, -1, 4 }, ExpectedResult = 1 )]
+    public int CountSubarraysTest( int[] nums ) =>
+        new CountSubarraysOfLengthThreeWithACondition().CountSubarrays( nums );
+}