3392. Count Subarrays of Length Three With a Condition

MediumView on LeetCode

Array

Time: O(n)

Space: O(1)

Intuition

Count subarrays of length 4 with exactly 2 elements satisfying a property. Sliding window of size 4.

Algorithm

1Sliding window of size exactly 4. Count elements satisfying condition. Count windows with exactly 2.

Common Pitfalls

•Fixed window size 4. Slide across array, count qualifying windows.

3392.cs

// Approach: Scan all length-3 windows; check if middle == (left + right) / 2.
// Time: O(n) Space: O(1)

public class Solution
{
    public int CountSubarrays(int[] nums)
    {
        int ans = 0;

        for (int i = 1; i + 1 < nums.Length; ++i)
        {
            if (nums[i] == (nums[i - 1] + nums[i + 1]) * 2)
                ++ans;
        }

        return ans;
    }
}

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