（HDU - 1800）Flying to the Mars

（HDU - 1800）Flying to the Mars

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 21147 Accepted Submission(s): 6825

Problem Description

In the year 8888, the Earth is ruled by the PPF Empire . As the population growing , PPF needs to find more land for the newborns . Finally , PPF decides to attack Kscinow who ruling the Mars . Here the problem comes! How can the soldiers reach the Mars ? PPF convokes his soldiers and asks for their suggestions . “Rush … ” one soldier answers. “Shut up ! Do I have to remind you that there isn’t any road to the Mars from here!” PPF replies. “Fly !” another answers. PPF smiles :“Clever guy ! Although we haven’t got wings , I can buy some magic broomsticks from HARRY POTTER to help you .” Now , it’s time to learn to fly on a broomstick ! we assume that one soldier has one level number indicating his degree. The soldier who has a higher level could teach the lower , that is to say the former’s level > the latter’s . But the lower can’t teach the higher. One soldier can have only one teacher at most , certainly , having no teacher is also legal. Similarly one soldier can have only one student at most while having no student is also possible. Teacher can teach his student on the same broomstick .Certainly , all the soldier must have practiced on the broomstick before they fly to the Mars! Magic broomstick is expensive !So , can you help PPF to calculate the minimum number of the broomstick needed .
For example :
There are 5 soldiers (A B C D E)with level numbers : 2 4 5 6 4;
One method :
C could teach B; B could teach A; So , A B C are eligible to study on the same broomstick.
D could teach E;So D E are eligible to study on the same broomstick;
Using this method , we need 2 broomsticks.
Another method:
D could teach A; So A D are eligible to study on the same broomstick.
C could teach B; So B C are eligible to study on the same broomstick.
E with no teacher or student are eligible to study on one broomstick.
Using the method ,we need 3 broomsticks.
……

After checking up all possible method, we found that 2 is the minimum number of broomsticks needed.

Input

Input file contains multiple test cases.
In a test case,the first line contains a single positive number N indicating the number of soldiers.(0<=N<=3000)
Next N lines :There is only one nonnegative integer on each line , indicating the level number for each soldier.( less than 30 digits);

Output

For each case, output the minimum number of broomsticks on a single line.

Sample Input

4
10
20
30
04
5
2
3
4
3
4

Sample Output

1
2

题目大意：有n个人，每个人都有一个等级，等级高的人可以交等级低的人飞行，一个老师只能有一个学生，一个学生也只能有一个老师，当然也可以没有。老师可以再同一个扫帚上教学生，所有人都要学会飞，问最少需要购买多少把扫帚。

思路：乍一看很麻烦，其实只是题目长了点，读懂题目就是一道大水题，利用贪心思想，实质就是求有相同等级的人最多是多少。

#include
#include
using namespace std;

const int INF=0x3f3f3f3f;
const int maxn=3005;
int a[maxn];

int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        for(int i=0;iscanf("%d",a+i);
        sort(a,+a+n);//切记使用STL中的二分查找函数一定要先排序 
        int ans=-INF;
        for(int i=0;iint(upper_bound(a,a+n,a[i])-lower_bound(a,a+n,a[i])));
        printf("%d\n",ans);
    }
    return 0;
}