3206. Alternating Groups I

Problem Link

Description

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There is a circle of red and blue tiles. You are given an array of integers colors. The color of tile i is represented by colors[i]:

• colors[i] == 0 means that tile i is red.
• colors[i] == 1 means that tile i is blue.

Every 3 contiguous tiles in the circle with alternating colors (the middle tile has a different color from its left and right tiles) is called an alternating group.

Return the number of alternating groups.

Note that since colors represents a circle, the first and the last tiles are considered to be next to each other.

 

Example 1:

Input: colors = [1,1,1]

Output: 0

Explanation:

Example 2:

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

Output: 3

Explanation:

Alternating groups:

 

Constraints:

• 3 <= colors.length <= 100
• 0 <= colors[i] <= 1

Solution

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Python3

class Solution:
    def numberOfAlternatingGroups(self, colors: List[int]) -> int:
        N = len(colors)
        res = 0
        
        for i in range(N):
            left = N - 1 if i == 0 else i - 1
            right = 0 if i == N - 1 else i + 1
            
            if colors[i] != colors[left] and colors[i] != colors[right]:
                res += 1
        
        return res