Longest Increasing Subsequence

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

For example, Given [10, 9, 2, 5, 3, 7, 101, 18], The longest increasing subsequence is [2, 3, 7, 101], therefore the length is 4. Note that 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(object):
    def lengthOfLIS(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if not nums:
            return 0
        dp = [1 for _ in range(len(nums))]
        for i in range(1, len(nums)):
            for j in range(i-1,-1,-1):
                if nums[i] > nums[j] and dp[i] < dp[j] + 1:
                    dp[i] = dp[j] + 1
        return max(dp)

Improved Solution

class Solution(object):
    def lengthOfLIS(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        dp = []
        for num in nums:
            pos = bisect.bisect_left(dp, num)
            if pos == len(dp):
                dp += num,
            else:
                dp[pos] = num
        return len(dp)