【朱迪的LeetCode刷题笔记】】334. Increasing Triplet Subsequence #Medium #Python

Judie

Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and nums<i> < nums[j] < nums[k]. If no such indices exists, return false.

Example 1:
Input: nums = [1,2,3,4,5]
Output: true
Explanation: Any triplet where i < j < k is valid.

Example 2:
Input: nums = [5,4,3,2,1]
Output: false
Explanation: No triplet exists.

Example 3:
Input: nums = [2,1,5,0,4,6]
Output: true
Explanation: The triplet (3, 4, 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6.

Constraints:
1 <= nums.length <= 5 * 105
-231 <= nums<i> <= 231 - 1

Follow up:
Could you implement a solution that runs in O(n) time complexity and O(1) space complexity?

Judy
Python taught by Mike

1. 
   
2. class Solution(object):
   
3.     def increasingTriplet(self, nums):
   
4.         """
   
5.         :type nums: List[int]
   
6.         :rtype: bool
   
7.         """
   
8.         i = None
   
9.         j = None
   
10.         for n in nums:
    
11.             if i == None or n < i:
    
12.                 i = n
    
13.             elif j == None:
    
14.                 if n > i:
    
15.                     j = n   
    
16.                 else:
    
17.                     continue
    
18.             elif n > j:
    
19.                 return True   
    
20.             elif i < n < j:
    
21.                 j = n
    
22.         return False
    

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Sol1
Python
https://leetcode.com/problems/in ... p;envId=leetcode-75

1. def increasingTriplet(nums):
   
2.     first = second = float('inf')
   
3.     for n in nums:
   
4.         if n <= first:
   
5.             first = n
   
6.         elif n <= second:
   
7.             second = n
   
8.         else:
   
9.             return True
   
10.     return False

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