1248. Count Number of Nice Subarrays

Problem Link

Description

---

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 are 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

---

Python3

class Solution:
    def numberOfSubarrays(self, nums: List[int], k: int) -> int:
        N = len(nums)
        
        def atMost(k):
            res = odds = i = 0
            
            for j, x in enumerate(nums):
                odds += int(x & 1)
 
                while odds > k:
                    odds -= int(nums[i] & 1)
                    i += 1
                
                res += (j - i + 1)
 
            return res
        
        return atMost(k) - atMost(k - 1)