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LeetCode solutions

2870. Longest Alternating Subarray

My accepted Python solution to LeetCode problem 2870, Longest Alternating Subarray, running in 59ms.

  • Difficulty: Easy
  • Python
  • Runtime 59ms
  • Memory 17.3MB

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 59ms, memory 17.3MB, accepted 2025-12-31.

python
class Solution:
    def alternatingSubarray(self, nums: List[int]) -> int:
        n = len(nums)
        max_len = -1
        for i in range(n - 1):
            if nums[i + 1] - nums[i] == 1:
                length = 2
                expected = -1
                j = i + 2
                while j < n and nums[j] - nums[j - 1] == expected:
                    length += 1
                    expected *= -1
                    j += 1
                max_len = max(max_len, length)
        return max_len

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