Longest Subsequence

Problem

Given an integer array nums, return the length of the longest subsequence where the subsequence first strictly increases and then strictly decreases.

A subsequence is a sequence that can be derived from the array by deleting some or no elements without changing the order of the remaining elements.

Examples

longestSubsequence([1, 2, 1])
// returns 3
// The longest subsequence is [1, 2, 1],
// which increases and then decreases

longestSubsequence([1, 8, 7, 4, 9, 3, 2])
// returns 6
// The longest subsequence is [1, 8, 7, 4, 3, 2],
// which first increases to 8, then decreases to 2