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LeetCode solutions

3483. Alternating Groups II

My accepted Python solution to LeetCode problem 3483, Alternating Groups II, running in 737ms.

  • Difficulty: Medium
  • Python
  • Runtime 737ms
  • Memory 21.2MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 737ms, memory 21.2MB, accepted 2025-12-30.

python
class Solution:
    def numberOfAlternatingGroups(self, colors: List[int], k: int) -> int:
        n = len(colors)
        # Extend the array to handle circular nature
        extended = colors + colors[:k-1]
        
        count = 0
        streak = 1  # length of current alternating sequence
        
        for i in range(1, len(extended)):
            if extended[i] != extended[i-1]:
                streak += 1
            else:
                streak = 1
            
            # Check if we have a valid alternating group of size k
            if streak >= k and i >= k - 1 and i < n + k - 1:
                if i - k + 1 < n:  # Starting position is in original array
                    count += 1
        
        return count

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