Problem

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

using Arrays.binarySearch(int[] array, int start, int end, int target)

class Solution {
    public int lengthOfLIS(int[] nums) {
        int[] dp = new int[nums.length];
        int len = 0;
        for(int x: nums) {
            int i = Arrays.binarySearch(dp, 0, len, x);
            if (i < 0) {
                i = -i-1;
                dp[i] = x;
            }
            if (i == len) len++;
        }
        return len;
    }
}