Today I have done leetcode's June LeetCoding Challenge with cpp.

June LeetCoding Challenge 22

Description

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 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

class Solution {
public:
  int numberOfSubarrays(vector<int>& nums, int k) {
    for(auto &n : nums) {
      n %= 2;
    }

    vector<int> prefix(nums.size() + 1);
    prefix[0] = 1;
    int s = 0;
    int answer = 0;
    for(int i = 0; i < nums.size(); ++i) {
      s += nums[i];
      answer += (s >= k) ? prefix[s - k] : 0;
      prefix[s] += 1;
    }

    return answer;
  }
};