【代码超详解】POJ 3250 Bad Hair Day（单调栈，219 ms）

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于 2020-02-05 23:24:01 发布 · 375 阅读

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这篇博客介绍了POJ 3250 Bad Hair Day问题，这是一个关于计算每头牛能看到多少头比它矮的牛的题目。博主通过单调栈的算法分析，给出了详细的问题描述、输入输出格式，并提供了AC代码，代码运行时间为219 ms。

一、题目描述

Bad Hair Day

Time Limit: 2000MS Memory Limit: 65536K
Total Submissions: 27077 Accepted: 9287（2020/2/5 23:27）

Description

Some of Farmer John’s N cows (1 ≤ N ≤ 80,000) are having a bad hair day! Since each cow is self-conscious about her messy hairstyle, FJ wants to count the number of other cows that can see the top of other cows’ heads.

Each cow i has a specified height hi (1 ≤ hi ≤ 1,000,000,000) and is standing in a line of cows all facing east (to the right in our diagrams). Therefore, cow i can see the tops of the heads of cows in front of her (namely cows i+1, i+2, and so on), for as long as these cows are strictly shorter than cow i.

Consider this example:

在这里插入图片描述

Cow#1 can see the hairstyle of cows #2, 3, 4
Cow#2 can see no cow’s hairstyle
Cow#3 can see the hairstyle of cow #4
Cow#4 can see no cow’s hairstyle
Cow#5 can see the hairstyle of cow 6
Cow#6 can see no cows at all!

Let ci denote the number of cows whose hairstyle is visible from cow i; please compute the sum of c1 through cN.For this example, the desired is answer 3 + 0 + 1 + 0 + 1 + 0 = 5.