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

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

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 = [1,1,1,1,1], k = 1, threshold = 0
Output: 5

Example 3:

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.

Example 4:

Input: arr = [7,7,7,7,7,7,7], k = 7, threshold = 7
Output: 1

Example 5:

Input: arr = [4,4,4,4], k = 4, threshold = 1
Output: 1

 

Constraints:

• 1 <= arr.length <= 10^5
• 1 <= arr[i] <= 10^4
• 1 <= k <= arr.length
• 0 <= threshold <= 10^4

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/number-of-sub-arrays-of-size-k-and-average-greater-than-or-equal-to-threshold/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int numOfSubarrays(vector<int>& arr, int k, int threshold) {
        int sum = 0, cnt = 0;
        for (int i = 0; i < arr.size(); ++i) {
            sum += arr[i];
            if (i >= k) sum -= arr[i - k];
            if (i + 1 >= k && sum / k >= threshold) ++cnt;
        }
        return cnt;
    }
};