3685 Count Subarrays Of Length Three With A Condition

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

class Solution:
    def countSubarrays(self, nums: List[int]) -> int:
        left = 0
        right = 2
        res = 0
        while(right < len(nums)):
            if 2 * (nums[left] + nums[right]) == nums[left + 1]:
                res += 1
            left += 1
            right += 1

        return res