LeetCode //C - 1248. Count Number of Nice Subarrays

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 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 <= numsi <= 10^5
• 1 <= k <= nums.length

From: LeetCode

Link: 1248. Count Number of Nice Subarrays

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Solution:

Ideas:

count subarrays with exactly k odds = subarrays with at most k odds − subarrays with at most k-1 odds.

Code:

int atMostKOdds(int* nums, int numsSize, int k) {
    if (k < 0) return 0;

    int left = 0;
    int countOdd = 0;
    int ans = 0;

    for (int right = 0; right < numsSize; right++) {
        if (nums[right] % 2 == 1) {
            countOdd++;
        }

        while (countOdd > k) {
            if (nums[left] % 2 == 1) {
                countOdd--;
            }
            left++;
        }

        ans += right - left + 1;
    }

    return ans;
}

int numberOfSubarrays(int* nums, int numsSize, int k) {
    return atMostKOdds(nums, numsSize, k) - atMostKOdds(nums, numsSize, k - 1);
}