【leetcode】Increasing Triplet Subsequence

Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.

Formally the function should:

Return true if there exists i, j, k
such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n-1 else return false.

Your algorithm should run in O(n) time complexity and O(1) space complexity.

Examples:
Given [1, 2, 3, 4, 5],
return true.

Given [5, 4, 3, 2, 1],
return false.

 

解题思路：遍历数组，遍历过程中更新已经遍历的数组元素中的最小值和次小值，如果后续有元素比这两个值都大，说明存在这样的一个递增子序列。

class Solution(object):
    def increasingTriplet(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        min = 9999999999
        smin = 9999999999
        for i in nums:
            if i < min:
                min = i
            elif i<smin:
                smin = i
            else:
                return True
        return False