Back to course home

0% completed

# Solution: Longest Alternating Subsequence

## Problem Statement

Given a number sequence, find the length of its Longest Alternating Subsequence (LAS). A subsequence is considered alternating if its elements are in alternating order.

A three element sequence (a1, a2, a3) will be an alternating sequence if its elements hold one of the following conditions:

```
{a1 > a2 < a3 } or { a1 < a2 > a3}.
```

**Example 1:**

```
Input: {1,2,3,4}
Output: 2
Explanation: There are many LAS: {1,2}, {3,4}, {1,3}, {1,4}
```

**Example 2:**

```
Input: {3,2,1,4}
Output: 3
Explanation: The LAS are {3,2,4} and {2,1,4}.
```

**Example 3:**

.....

.....

.....

Like the course? Get enrolled and start learning!