3208. Alternating Groups II

Problem Link

Description

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There is a circle of red and blue tiles. You are given an array of integers colors and an integer k. 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.

An alternating group is every k contiguous tiles in the circle with alternating colors (each tile in the group except the first and last one has a different color from its left and right tiles).

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 = [0,1,0,1,0], k = 3

Output: 3

Explanation:

Alternating groups:

Example 2:

Input: colors = [0,1,0,0,1,0,1], k = 6

Output: 2

Explanation:

Alternating groups:

Example 3:

Input: colors = [1,1,0,1], k = 4

Output: 0

Explanation:

 

Constraints:

• 3 <= colors.length <= 105
• 0 <= colors[i] <= 1
• 3 <= k <= colors.length

Solution

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Python3

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