1248. Count Number of Nice Subarrays

Medium

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

Solution:

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

Constraints:

class Solution {

    /**
     * @param Integer[] $nums
     * @param Integer $k
     * @return Integer
     */
    function numberOfSubarrays($nums, $k) {
        $r  = array(0, 0);
        $res = 0;
        $pre = 0;
        $cur = 0;
        for($i = 0; $i < count($nums); $i++){
            $r[$nums[$i] & 1]++;
            if($r[1] == $k){
                $pre = $cur;
            }
            while($r[1] == $k){
                $r[$nums[$cur] & 1]--;
                $cur++;
            }    
            $res += $cur - $pre;
        }
        return $res;
    }
}

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