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

Problem

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 <= 10^5

• 1 <= arr[i] <= 10^4

• 1 <= k <= arr.length

• 0 <= threshold <= 10^4

Solution (Java)

class Solution {
    public int numOfSubarrays(int[] arr, int k, int threshold) {
        int sum = 0;
        for (int i = 0; i < k - 1; i++) {
            sum += arr[i];
        }
        int count = 0;
        for (int i = k - 1; i < arr.length; i++) {
            sum += arr[i];
            if (i - k >= 0) {
                sum -= arr[i - k];
            }
            if (sum / k >= threshold) {
                count++;
            }
        }
        return count;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).