最新消息:点击查看大S的省钱秘笈

POJ 2431 Expedition C++版

POJ题解 Slyar 85浏览 0评论

文章作者:姜南(Slyar) 文章来源:Slyar Home (www.slyar.com) 转载请注明,谢谢合作。

贪心算法

Description

A group of cows grabbed a truck and ventured on an expedition deep into the jungle. Being rather poor drivers, the cows unfortunately managed to run over a rock and puncture the truck's fuel tank. The truck now leaks one unit of fuel every unit of distance it travels.

To repair the truck, the cows need to drive to the nearest town (no more than 1,000,000 units distant) down a long, winding road. On this road, between the town and the current location of the truck, there are N (1 <= N <= 10,000) fuel stops where the cows can stop to acquire additional fuel (1..100 units at each stop).

The jungle is a dangerous place for humans and is especially dangerous for cows. Therefore, the cows want to make the minimum possible number of stops for fuel on the way to the town. Fortunately, the capacity of the fuel tank on their truck is so large that there is effectively no limit to the amount of fuel it can hold. The truck is currently L units away from the town and has P units of fuel (1 <= P <= 1,000,000).

Determine the minimum number of stops needed to reach the town, or if the cows cannot reach the town at all.

Input

* Line 1: A single integer, N

* Lines 2..N+1: Each line contains two space-separated integers describing a fuel stop: The first integer is the distance from the town to the stop; the second is the amount of fuel available at that stop.

* Line N+2: Two space-separated integers, L and P

Output

* Line 1: A single integer giving the minimum number of fuel stops necessary to reach the town. If it is not possible to reach the town, output -1.

Sample Input

4
4 4
5 2
11 5
15 10
25 10

Sample Output

2

Slyar:加油站问题的进阶版,经典加油站问题每个加油站加的油是一样多的,而这里每个加油站加的油是不一样的,很容易考虑到贪心策略是在以前的基础上选择一个加油量最大的加油站加油,因为这样可以开得更远...反正很简单啦。

一开始我直接用N^2的算法写,也过了,后来看到说可以用大堆来维护油量,豁然开朗...最近在学C++,抱着玩的思想,写了一个STL版本,太爽了...我居然还重载了<操作符,哇咔咔...

转载请注明:Slyar Home » POJ 2431 Expedition C++版

发表我的评论
取消评论

表情

Hi,您需要填写昵称和邮箱!

  • 昵称 (必填)
  • 邮箱 (必填)
  • 网址

网友最新评论 (1)

  1. 嘿嘿,我也正在搞这个,不过菜鸟一只,等过些时间想和你交换连接可否?到时再说,现在还不够资格!o(∩_∩)o 哈哈!拓扑式逛博客,转到这里,新手建博,前来留个脚印!
    砖头7年前 (2010-06-18)回复