LeetCode 456. 132 Pattern

junchen1992

于 2017-01-08 22:21:53 发布

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分类专栏：算法 LeetCode 文章标签： Stack

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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 $a_1, a_2, ..., a_n$ , a 132 pattern is a subsequence $a_i, a_j, a_k$ such that $i < j < k$ and $a_i < a_k < a_j$ . 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].

LeetCode 456. 132 Pattern

Problem Statement

Solution