Increasing Triplet Subsequence

描述

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

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

Your function 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.

分析

扫描一遍数组,用变量x1保存当前最小的值,变量x2保存当前第二小的值。如果右面能碰到一个数大于x2,说明必然存在一个递增的三元组。

代码

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