Problem 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.
Key Insights
- A subarray of length 3 can be represented as
nums[i], nums[i+1], nums[i+2]. - For each valid subarray, we need to check if
nums[i] + nums[i+2] == nums[i+1] / 2. - The sum of the first and third elements must equal half of the middle element.
- The constraints allow for a straightforward O(n) solution due to the small maximum length of the array.
Space and Time Complexity
Time Complexity: O(n)
Space Complexity: O(1)
Solution
To solve the problem, we iterate through the array from the beginning to the third-to-last element. For each set of three consecutive elements, we check the condition: if the sum of the first and third elements equals half of the second element. If the condition is satisfied, we increment our count. This approach uses constant space and runs in linear time relative to the input size.