2962. Count Subarrays Where Max Element Appears at Least K Times

Problem Link

Description

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You are given an integer array nums and a positive integer k.

Return the number of subarrays where the maximum element of nums appears at least k times in that subarray.

A subarray is a contiguous sequence of elements within an array.

 

Example 1:

Input: nums = [1,3,2,3,3], k = 2
Output: 6
Explanation: The subarrays that contain the element 3 at least 2 times are: [1,3,2,3], [1,3,2,3,3], [3,2,3], [3,2,3,3], [2,3,3] and [3,3].

Example 2:

Input: nums = [1,4,2,1], k = 3
Output: 0
Explanation: No subarray contains the element 4 at least 3 times.

 

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i] <= 106
• 1 <= k <= 105

Solution

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Python3

class Solution:
    def countSubarrays(self, nums: List[int], k: int) -> int:
        N = len(nums)
        maxNum = max(nums)
        total = N * (N + 1) // 2
        i = 0
        count = 0
        res = 0 # represents the number of subarrays where the freq of maxNum < k
 
        for j, x in enumerate(nums):
            if x == maxNum:
                count += 1
            
            while count >= k:
                if nums[i] == maxNum:
                    count -= 1
                
                i += 1
            
            res += j - i + 1
        
        return total - res