Count Subarrays of Length Three With a Condition

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Question

Approach

When solving this, I noticed that I only needed to check all subarrays of length 3. So I iterated over the array, looking at every group of three consecutive numbers. For each triplet, I checked if the sum of the first and third numbers was exactly half of the second number. If the condition was satisfied, I incremented my answer counter.

Implementation

class Solution:
    def countSubarrays(self, nums: List[int]) -> int:
        count = 0
        n = len(nums)
        
        for i in range(n - 2):
            if nums[i] + nums[i + 2] == nums[i + 1] / 2:
                count += 1
        
        return count

Complexities

• Time: O(n)
• Space: O(1)