HDU 4442 Physical Examination

Physical Examination

Time Limit: 1000ms

Memory Limit: 32768KB

This problem will be judged on HDU. Original ID: 4442
64-bit integer IO format: %I64d      Java class name: Main

 

WANGPENG is a freshman. He is requested to have a physical examination when entering the university.
Now WANGPENG arrives at the hospital. Er….. There are so many students, and the number is increasing!
There are many examination subjects to do, and there is a queue for every subject. The queues are getting longer as time goes by. Choosing the queue to stand is always a problem. Please help WANGPENG to determine an exam sequence, so that he can finish all the physical examination subjects as early as possible.

 

Input

There are several test cases. Each test case starts with a positive integer n in a line, meaning the number of subjects(queues).
Then n lines follow. The i-th line has a pair of integers (ai, bi) to describe the i-th queue:
1. If WANGPENG follows this queue at time 0, WANGPENG has to wait for ai seconds to finish this subject.
2. As the queue is getting longer, the waiting time will increase bi seconds every second while WANGPENG is not in the queue.
The input ends with n = 0.
For all test cases, 0<n≤100000, 0≤ai,bi<231.

 

Output

For each test case, output one line with an integer: the earliest time (counted by seconds) that WANGPENG can finish all exam subjects. Since WANGPENG is always confused by years, just print the seconds mod 365×24×60×60.

 

Sample Input

5
1 2
2 3
3 4
4 5
5 6
0

Sample Output

1419

Hint

In the Sample Input, WANGPENG just follow the given order. He spends 1 second in the first queue, 5 seconds in the 2th queue, 27 seconds in the 3th queue, 169 seconds in the 4th queue, and 1217 seconds in the 5th queue. So the total time is 1419s. WANGPENG has computed all possible orders in his 120-core-parallel head, and decided that this is the optimal choice.

Source

2012 Asia JinHua Regional Contest

 

解题：贪心。贪心策略就是：假设先选1号，再选2号项目，那么有　　a₁ + a₁*b₂ + b₂ < a₂ + a₂b₁ + a_1 .

 

这样排完序即可。

 

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <climits>
#include <vector>
#include <queue>
#include <cstdlib>
#include <string>
#include <set>
#include <stack>
#define LL long long
#define pii pair<int,int>
#define INF 0x3f3f3f3f
using namespace std;
const int maxn = 100010;
const LL mod = 365*24*60*60;
struct node{
    int x,y;
};
node e[maxn];
bool cmp(const node &a,const node &b){
    return (LL)a.x*b.y < (LL)b.x*a.y;
}
int main() {
    int n;
    LL ans;
    while(scanf("%d",&n),n){
        for(int i = 0; i < n; i++)
            scanf("%d %d",&e[i].x,&e[i].y);
        sort(e,e+n,cmp);
        ans = e[0].x;
        for(int i = 1; i < n; i++){
            ans += (e[i].x + ans*e[i].y)%mod;
            ans %= mod;
        }
        printf("%I64d
",ans);
    }
    return 0;
}