1248. Count Number of Nice Subarrays

Given an array of integers `nums` and an integer `k`. A continuous subarray is called nice if there are `k` odd numbers on it.

Return the number of nice sub-arrays.

Example 1:

```Input: nums = [1,1,2,1,1], k = 3
Output: 2
Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].
```

Example 2:

```Input: nums = [2,4,6], k = 1
Output: 0
Explanation: There is no odd numbers in the array.
```

Example 3:

```Input: nums = [2,2,2,1,2,2,1,2,2,2], k = 2
Output: 16
```

Constraints:

• `1 <= nums.length <= 50000`
• `1 <= nums[i] <= 10^5`
• `1 <= k <= nums.length`

1248. Count Number of Nice Subarrays
``````struct Solution;

impl Solution {
fn number_of_subarrays(nums: Vec<i32>, k: i32) -> i32 {
let n = nums.len();
let mut count = vec![0; n + 1];
let k = k as usize;
count[0] = 1;
let mut prev = 0;
let mut res = 0;
for i in 0..n {
if nums[i] % 2 == 1 {
prev += 1;
}
count[prev] += 1;
if prev >= k {
res += count[prev - k];
}
}
res as i32
}
}

#[test]
fn test() {
let nums = vec![1, 1, 2, 1, 1];
let k = 3;
let res = 2;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
let nums = vec![2, 4, 6];
let k = 1;
let res = 0;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
let nums = vec![2, 2, 2, 1, 2, 2, 1, 2, 2, 2];
let k = 2;
let res = 16;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
}
``````