LeetCode 456. 132 Pattern

本文介绍了一种用于检测特定序列中是否存在132模式的算法。132模式是指在一个序列中找到三个数a_i, a_j, a_k,满足i < j < k且a_i < a_k < a_j的条件。文章通过示例展示了如何应用该算法来判断给定序列是否含有132模式。

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Problem Statement

(Source) Given a sequence of n integers a1,a2,...,an , a 132 pattern is a subsequence ai,aj,ak such that i<j<k and ai<ak<aj . Design an algorithm that takes a list of n numbers as input and checks whether there is a 132 pattern in the list.

Note: n will be less than 15,000.

Example 1:

Input: [1, 2, 3, 4]

Output: False

Explanation: There is no 132 pattern in the sequence.

Example 2:

Input: [3, 1, 4, 2]

Output: True

Explanation: There is a 132 pattern in the sequence: [1, 4, 2].

Example 3:

Input: [-1, 3, 2, 0]

Output: True

Explanation: There are three 132 patterns in the sequence: [-1, 3, 2], [-1, 3, 0] and [-1, 2, 0].

Solution

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