[064] LeetCode 334演算法【Increasing Triplet Subsequence】遞增三元子序列

334. Increasing Triplet Subsequence (Medium)

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.

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

Example 1:

Input: [1,2,3,4,5]
Output: true

Example 2:

Input: [5,4,3,2,1]
Output: false

這題直接做兩個數字當成第一個跟第二個，之後只要判斷你比第二個數大就表示找到三個數字了，這題有點過於簡單，但臉書、谷歌、亞麻、雅虎都考過這道題。

大家加油。

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