300. Longest Increasing Subsequence

Posted 2020-11-14 wentiliangkaihua

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?

class Solution {
    public int lengthOfLIS(int[] nums) {
        int l = nums.length;
        if(l == 0) return 0;
        int[] f = new int[l];
        int res = 1;
        Arrays.fill(f,1);
        for(int j = 1; j < l; j++){
            for(int i = 0; i < j; i++){
                if(nums[j] > nums[i]){
                    f[j] = Math.max(f[j], f[i] + 1);
                }
            }
            res = Math.max(res, f[j]);
        }
        return res;
    }
}