Leetcode 1343. Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold

Problem statement

https://leetcode.com/problems/number-of-sub-arrays-of-size-k-and-average-greater-than-or-equal-to-threshold/

Solution

Just use accumulate, then we can calculate sums in all n - k + 1 subarrays of size k fast.

Complexity

It is O(n) for time and space.

Code

class Solution:
    def numOfSubarrays(self, arr, k, threshold):
        acc = [0] + list(accumulate(arr))
        return sum(acc[i + k] - acc[i] >= threshold * k for i in range(len(arr) - k + 1))