# Problem Definition

## Description

Given an array of integers, find the length of longest subsequence which is first increasing then decreasing.

**Example:**

For the given array `[1 11 2 10 4 5 2 1]`

Longest subsequence is `[1 2 10 4 2 1]`

Return value 6

## Notes

1. [YT video - Vivekanand Khyade - Longest Increasing Subsequence (Dynamic Programming)](https://www.youtube.com/watch?v=E6us4nmXTHs)
1. [YT video - Tushar Roy - Longest Increasing Subsequence](https://www.youtube.com/watch?v=CE2b_-XfVDk)
1. [YT video - Tushar Roy - Longest Increasing Subsequence in n*log(n) time](https://www.youtube.com/watch?v=S9oUiVYEq7E)