Given an array of integers nums and an integer k. A 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
Solution:
func numberOfSubarrays(nums []int, k int) int {
n := len(nums)
var count, odd, l, r int
for r < n {
if nums[r] & 1 == 1 {
odd++
}
r++
if odd == k {
tmp := r
for r < n && nums[r] & 1 == 0 {
r++
}
lEven, rEven := 0, r - tmp
for nums[l] & 1 == 0 {
lEven++
l++
}
count += (lEven + 1) * (rEven + 1)
l++
odd--
}
}
return count
}