Longest Increasing Subsequence

Given an unsorted array of integers, find the length of longest increasing subsequence.

Example:

Input: [10,9,2,5,3,7,101,18]
Output: 4 
Explanation: The longest increasing subsequence is [2,3,7,101], therefore the length is 4.

Note:

There may be more than one LIS combination, it is only necessary for you to return the length.
Your algorithm should run in O(n2) complexity.

Follow up: Could you improve it to O(n log n) time complexity?

Solution:

class Solution {
    public int lengthOfLIS(int[] nums) {
        TreeSet<Integer> seq = new TreeSet();
        for (int val : nums) {
            Integer bigger = seq.ceiling(val);
            if (bigger != null) {
                seq.remove(bigger);
            }
            seq.add(val);
        }
        return seq.size();
    }
}