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POJ 1922 Ride to School C语言版

POJ题解 Slyar 116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。

简单贪心

Description

Many graduate students of Peking University are living in Wanliu Campus, which is 4.5 kilometers from the main campus – Yanyuan. Students in Wanliu have to either take a bus or ride a bike to go to school. Due to the bad traffic in Beijing, many students choose to ride a bike.

We may assume that all the students except "Charley" ride from Wanliu to Yanyuan at a fixed speed. Charley is a student with a different riding habit – he always tries to follow another rider to avoid riding alone. When Charley gets to the gate of Wanliu, he will look for someone who is setting off to Yanyuan. If he finds someone, he will follow that rider, or if not, he will wait for someone to follow. On the way from Wanliu to Yanyuan, at any time if a faster student surpassed Charley, he will leave the rider he is following and speed up to follow the faster one.

We assume the time that Charley gets to the gate of Wanliu is zero. Given the set off time and speed of the other students, your task is to give the time when Charley arrives at Yanyuan.

Input

There are several test cases. The first line of each case is N (1 <= N <= 10000) representing the number of riders (excluding Charley). N = 0 ends the input. The following N lines are information of N different riders, in such format:

Vi [TAB] Ti

Vi is a positive integer <= 40, indicating the speed of the i-th rider (kph, kilometers per hour). Ti is the set off time of the i-th rider, which is an integer and counted in seconds. In any case it is assured that there always exists a nonnegative Ti.

Output

Output one line for each case: the arrival time of Charley. Round up (ceiling) the value when dealing with a fraction.

Sample Input

4
20    0
25    -155
27    190
30    240
2
21    0
22    34
0

Sample Output

780
771

Slyar:说下题目大意。大概就是说一个叫Charley的人在0秒的时候在Wanliu门口等同学骑单车载他去Yanyuan(题目中给出其他单车的速度以及出发时间),当有其他单车超过Charley时,他会跳上那辆快车继续前进,问最后Charley用了多长时间到达Yanyuan。

看到这题的描述中有"选择更快"的意思时,我就自觉往贪心上面想了,越想越觉得这题是贪心,因为每次Charley选择的都是当前最快的单车,而且Charley最后一定是和那个最快到达Yanyuan的单车同时到达。

无视负时间出发的单车(因为Charley还没到的时候单车就走了,他永远也追不上,所以我们只要看看比Charley晚出发的单车谁最快到达Yanyuan,让Charley跟着这辆车,最后的时间就是Charley到达的时间。

转载请注明:Slyar Home » POJ 1922 Ride to School C语言版

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网友最新评论 (2)

  1. @熟人Y 呵呵,Ylemzy,又换马甲了?
    Slyar7年前 (2009-09-01)回复
  2. 精度问题还是难以理解。我用 v /= 3.6; time += 4500.0 / v + t; 结果WR。
    熟人Y7年前 (2009-09-01)回复