hdu 4190 Distributing Ballot Boxes(贪心+二分查找)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4190

Distributing Ballot Boxes

Time Limit: 20000/10000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 1065    Accepted Submission(s): 536

Problem Description

Today, besides SWERC'11, another important event is taking place in Spain which rivals it in importance: General Elections. Every single resident of the country aged 18 or over is asked to vote in order to choose representatives for the Congress of Deputies and the Senate. You do not need to worry that all judges will suddenly run away from their supervising duties, as voting is not compulsory.
The administration has a number of ballot boxes, those used in past elections. Unfortunately, the person in charge of the distribution of boxes among cities was dismissed a few months ago due to nancial restraints. As a consequence, the assignment of boxes to cities and the lists of people that must vote in each of them is arguably not the best. Your task is to show how efficiently this task could have been done.
The only rule in the assignment of ballot boxes to cities is that every city must be assigned at least one box. Each person must vote in the box to which he/she has been previously assigned. Your goal is to obtain a distribution which minimizes the maximum number of people assigned to vote in one box.
In the first case of the sample input, two boxes go to the fi rst city and the rest to the second, and exactly 100,000 people are assigned to vote in each of the (huge!) boxes in the most efficient distribution. In the second case, 1,2,2 and 1 ballot boxes are assigned to the cities and 1,700 people from the third city will be called to vote in each of the two boxes of their village, making these boxes the most crowded of all in the optimal assignment.

 

Input

The fi rst line of each test case contains the integers N (1<=N<=500,000), the number of cities, and B(N<=B<=2,000,000), the number of ballot boxes. Each of the following N lines contains an integer a_i,(1<=a_i<=5,000,000), indicating the population of the i^th city.
A single blank line will be included after each case. The last line of the input will contain -1 -1 and should not be processed.

 

Output

For each case, your program should output a single integer, the maximum number of people assigned to one box in the most efficient assignment.

 

Sample Input

2 7

200000

500000

 

 

4 6

120

2680

3400

200

 

 

-1 -1

 

Sample Output

100000

1700

 

 

题目大意：有n个城市，b个投票箱，接下去的是每个城市的人口数，最后输出每个投票箱的容量是多少。

题目思路：对投票数进行二分，然后对箱子数进行匹配，人口数除以箱子的容量就是城市分配的箱子数。

 

详见代码。

#include <iostream>
#include <cstdio>
#include <cmath>

using namespace std;

int main ()
{
    int a[500001];
    int n,b,ans,Max;
    while (~scanf("%d%d",&n,&b))
    {
        if (n==-1&&b==-1)
            break;
        Max=0;
        for (int i=0;i<n;i++)
        {
            scanf("%d",&a[i]);
            if (Max<a[i])
                Max=a[i];
        }
        int l=0;
        int r=Max;
        int sum,mid;
        while (r>=l)
        {
            sum=0;
            mid=(r+l)/2;
            for (int i=0;i<n;i++)
            {
                sum+=ceil(a[i]*1.0/mid);
            }
            if (sum>b)
                l=mid+1;
            else
                r=mid-1,ans=mid;
        }
        printf ("%d
",ans);
    }
    return 0;
}