Description
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
Solution
Python3
class Solution:
def countSubarrays(self, nums: List[int]) -> int:
N = len(nums)
res = 0
for i in range(2, N):
first, second, third = nums[i - 2], nums[i - 1], nums[i]
if (first + third) * 2 == second:
res += 1
return res