LeetCode 334: Increasing Triplet Subsequence

Problem Description

LeetCode Problem 334

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

Difficulty: Medium

Tags: array, greedy

Rating: 93.39%

Solution

Here’s my Python solution to this problem:

class Solution:
    def increasingTriplet(self, nums: List[int]) -> bool:
        num1 = num2 = float('inf')

        for n in nums:
            if n <= num1:
                num1 = n
            elif n <= num2:
                num2 = n
            else:
                return True
        
        return False

Complexity Analysis

The solution has the following complexity characteristics:

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$

Note: This is an automated analysis and may not capture all edge cases or specific algorithmic optimizations.