Longest Increasing Subsequence

Question

## Problem

Find the length of the longest strictly increasing subsequence in an array.

## Example
```
[10,9,2,5,3,7,101,18] -> 4 ([2,3,7,101])
```

## Constraints
- 1 ≤ n ≤ 2500

## Approach
O(n^2) DP, or O(n log n) with patience sorting + binary search. Reported ServiceNow OA question.