文章标题 HDU 1445 ： Ride to School （贪心）

Ride to School

Problem 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

Source
Asia 2004, Beijing (Mainland China), Preliminary

题意： Charley骑自行车去学校，每次他都会跟着一个同学的速度一起去学校，如果遇到速度更大的同学，他就跟着速度快的那个同学，现在给出n个同学的骑车速度和开始出发的时间，问Charley最快到达学校的时间。
分析：但时间为负的时候，不用考虑，因为如果速度大 的肯定最不上，速度小的又不会跟着他，所以只需要求这n个同学到达学校的最短时间就是Charley到达学校的最短时间
代码：

#include<iostream>#include<string>#include<cstdio>#include<cstring>#include<vector>#include<math.h>#include<map>#include<queue> #include<algorithm>using namespace std;const int inf = 0x3f3f3f3f;int n;int main (){    while (scanf ("%d",&n)&&n){        double v,t;        double ans;        double tmp;        ans=999999999;        for (int i=0;i<n;i++){            scanf ("%lf%lf",&v,&t);            if (t<0)continue;            tmp=4.5*3600/v+t;            ans=min(ans,tmp);        }        if (ans>(int)ans) ans=ans+1;//不到一秒算一秒        printf ("%d\n",(int)ans);     }    return 0;}