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

Difficulty Topics

Description

Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.

 

Example 1:

Input: arr = [2,2,2,2,5,5,5,8], k = 3, threshold = 4
Output: 3
Explanation: Sub-arrays [2,5,5],[5,5,5] and [5,5,8] have averages 4, 5 and 6 respectively. All other sub-arrays of size 3 have averages less than 4 (the threshold).

Example 2:

Input: arr = [11,13,17,23,29,31,7,5,2,3], k = 3, threshold = 5
Output: 6
Explanation: The first 6 sub-arrays of size 3 have averages greater than 5. Note that averages are not integers.

 

Constraints:

  • 1 <= arr.length <= 105
  • 1 <= arr[i] <= 104
  • 1 <= k <= arr.length
  • 0 <= threshold <= 104

Solution

number-of-sub-arrays-of-size-k-and-average-greater-than-or-equal-to-threshold.py
class Solution:
    def numOfSubarrays(self, arr: List[int], k: int, threshold: int) -> int:
        n = len(arr)
        prefix = [0] * (n+1)
        res = 0

        for i,num in enumerate(arr):
            prefix[i+1] += prefix[i] + num

        for i in range(n-k+1):
            if (prefix[i+k] - prefix[i]) >= threshold * k:
                res += 1

        return res