leetcode_1343

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

Solutions

1. sliding window O(n) S(1)

class Solution {
public:
    int numOfSubarrays(vector<int>& arr, int k, int threshold) {
        threshold *= k;
        int sum = accumulate(arr.begin(), arr.begin() + k, 0);
        int num = sum >= threshold;

        for (int i = k; i < arr.size(); i++) {
            sum += arr[i] - arr[i - k];
            num += sum >= threshold;
        }

        return num;
    }
};

1. prefix sum