3101. Count Alternating Subarrays

Problem Link

Description

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You are given a binary array nums.

We call a subarray alternating if no two adjacent elements in the subarray have the same value.

Return the number of alternating subarrays in nums.

 

Example 1:

Input: nums = [0,1,1,1]

Output: 5

Explanation:

The following subarrays are alternating: [0], [1], [1], [1], and [0,1].

Example 2:

Input: nums = [1,0,1,0]

Output: 10

Explanation:

Every subarray of the array is alternating. There are 10 possible subarrays that we can choose.

 

Constraints:

• 1 <= nums.length <= 105
• nums[i] is either 0 or 1.

Solution

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Python3

class Solution:
    def countAlternatingSubarrays(self, nums: List[int]) -> int:
        N = len(nums)
        i = 0
        res = 0
        
        for j, x in enumerate(nums):
            if j > 0 and nums[j] == nums[j - 1]:
                i = j
                
            res += j - i + 1
        
        return res