Find the length of the longest strictly increasing subsequence in an array.
A subsequence keeps elements in order but can skip elements. It doesn't need to be contiguous.
With nums = [10,9,2,5,3,7,101,18]:
- Subsequence [2,3,7,101]: strictly increasing, length .
- Subsequence [2,5,7,18]: also length .
- No length-5 increasing subsequence exists.
- Answer: .
With nums = [0,1,0,3,2,3]:
- Subsequence [0,1,2,3]: length .
Constraints: nums.length .