Count Fixed-Length Windows Meeting an Average Threshold
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
Return the number of contiguous subarrays of exactly k elements whose arithmetic mean is at least threshold. Averages need not be integers.
```cpp
class Solution {
public:
int numOfSubarrays(vector<int>& arr, int k, int threshold);
};
```
### Examples
**Example 1:**
```text
Input: arr = [1,5,3,7], k = 2, threshold = 4
Output: 2
Explanation: Window sums are6,8,10. The last two meet the required sum8.
```
**Example 2:**
```text
Input: arr = [1,2], k = 2, threshold = 2
Output: 0
Explanation: The sole average is1.5, below2.
```
### Constraints
- arr has 1 to 100000 integers, each in `[1,10000]`.
- `1 <= k <= arr.length`.
- threshold is an integer in `[0,10000]`.
### Contract considerations
The window length is fixed at k, and threshold may be 0.
```hint Read the boundary condition
Check equality at the average threshold and windows covering the whole array. Every counted window has exactly the requested length.
```
### Boundary reminders
The window length is fixed at k, and threshold may be 0.
Overview: Count Fixed-Length Windows Meeting an Average Threshold. Return the number of contiguous subarrays of exactly k elements whose arithmetic mean is at least threshold.
