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g2701_2800.s2765_longest_alternating_subarray.readme.md Maven / Gradle / Ivy

2765\. Longest Alternating Subarray

Easy

You are given a **0-indexed** integer array `nums`. A subarray `s` of length `m` is called **alternating** if:

*   `m` is greater than `1`.
*   s1 = s0 + 1.
*   The **0-indexed** subarray `s` looks like [s0, s1, s0, s1,...,s(m-1) % 2]. In other words, s1 - s0 = 1, s2 - s1 = -1, s3 - s2 = 1, s4 - s3 = -1, and so on up to s[m - 1] - s[m - 2] = (-1)m.

Return _the maximum length of all **alternating** subarrays present in_ `nums` _or_ `-1` _if no such subarray exists__._

A subarray is a contiguous **non-empty** sequence of elements within an array.

**Example 1:**

**Input:** nums = [2,3,4,3,4]

**Output:** 4

**Explanation:** The alternating subarrays are [3,4], [3,4,3], and [3,4,3,4]. The longest of these is [3,4,3,4], which is of length 4. 

**Example 2:**

**Input:** nums = [4,5,6]

**Output:** 2

**Explanation:** [4,5] and [5,6] are the only two alternating subarrays. They are both of length 2. 

**Constraints:**

*   `2 <= nums.length <= 100`
*   1 <= nums[i] <= 104