mirror of
https://github.com/halfrost/LeetCode-Go.git
synced 2025-07-05 00:25:22 +08:00
47 lines
1.3 KiB
Markdown
Executable File
47 lines
1.3 KiB
Markdown
Executable File
# [456. 132 Pattern](https://leetcode.com/problems/132-pattern/)
|
||
|
||
|
||
## 题目
|
||
|
||
Given a sequence of n integers a1, a2, ..., an, 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].
|
||
|
||
|
||
## 题目大意
|
||
|
||
|
||
给定一个整数序列：a1, a2, ..., an，一个 132 模式的子序列 ai, aj, ak 被定义为：当 i < j < k 时，ai < ak < aj。设计一个算法，当给定有 n 个数字的序列时，验证这个序列中是否含有 132 模式的子序列。注意：n 的值小于 15000。
|
||
|
||
|
||
## 解题思路
|
||
|
||
|
||
- 这一题用暴力解法一定超时
|
||
- 这一题算是单调栈的经典解法，可以考虑从数组末尾开始往前扫，维护一个递减序列
|
||
|