Leetcode-300. Longest Increasing Subsequence

https://leetcode.com/problems/longest-increasing-subsequence/description/

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?

题解：dag动态规划模型，O(nlogn）没想到，看讨论是用二分搜索。

class Solution {
public:
    int lengthOfLIS(vector<int>& nums) {
      int l = nums.size();
      if (l <= 1){
        return l;
      }
      int ans = 1;
      vector<int> dp(l, 1);
      for (int i = 1; i < l; i++){
        for (int j = 0; j < i; j++){
          if (nums[j] < nums[i]){
            dp[i] = max(dp[i], dp[j] + 1);
          }
        }
        ans = max(ans, dp[i]);
      }
      return ans;
    }
};