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

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`

## Rust Solution

``````struct Solution;

impl Solution {
fn num_of_subarrays(arr: Vec<i32>, k: i32, threshold: i32) -> i32 {
let n = arr.len();
let mut prefix = vec![0; n + 1];
let sum = threshold * k;
let k = k as usize;
let mut res = 0;
for i in 0..n {
prefix[i + 1] = prefix[i] + arr[i];
}
for r in k..=n {
let l = r - k;
if prefix[r] - prefix[l] >= sum {
res += 1;
}
}
res
}
}

#[test]
fn test() {
let arr = vec![2, 2, 2, 2, 5, 5, 5, 8];
let k = 3;
let threshold = 4;
let res = 3;
assert_eq!(Solution::num_of_subarrays(arr, k, threshold), res);
let arr = vec![1, 1, 1, 1, 1];
let k = 1;
let threshold = 0;
let res = 5;
assert_eq!(Solution::num_of_subarrays(arr, k, threshold), res);
let arr = vec![11, 13, 17, 23, 29, 31, 7, 5, 2, 3];
let k = 3;
let threshold = 5;
let res = 6;
assert_eq!(Solution::num_of_subarrays(arr, k, threshold), res);
let arr = vec![7, 7, 7, 7, 7, 7, 7];
let k = 7;
let threshold = 7;
let res = 1;
assert_eq!(Solution::num_of_subarrays(arr, k, threshold), res);
let arr = vec![4, 4, 4, 4];
let k = 4;
let threshold = 1;
let res = 1;
assert_eq!(Solution::num_of_subarrays(arr, k, threshold), res);
}
``````

Having problems with this solution? Click here to submit an issue on github.