leetcode300 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.
"""
"""
类似于139，322
自己找到了动态规划方程
f(i) = 1 + max(f(j) if nums[i] > nums[j]) (j < i)
特别注意的是将数组初始化为1
"""
class Solution:
    def lengthOfLIS(self, nums):
        if not nums: #bug nums == None 无法通过 nums = []的情况
            return 0
        dp = [1] * (len(nums)+1)
        for i in range(1, len(nums)):
            for j in range(i):
                if nums[j] < nums[i]:
                    dp[i] = max(dp[i], dp[j] + 1)
        return max(dp)

# nums1 = None
# nums2 = []
# if nums1 == None:
#     print('1')
# if not nums1:
#     print('2')
# if nums2 == None: #针对这种情况无法判断nums=[]
#     print('3')
# if not nums2:
#     print('4')
# #Answer 为 1 2 4