Distributing Ballot Boxes HDU

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
const int N = 500010;
int arr[N];
int city,box;
bool check(int mid)
{
	int sum = 0;
	for (int i = 0; i < city; i++)
		//最大箱子的容量
		sum += ceil(arr[i]*1.0/mid);
	return sum<=box;
}
int main()
{
	while (scanf("%d%d",&city,&box) != EOF)
	{
		if (city == -1 && box == -1)
			break;
		int res = 0;
		for (int i = 0; i < city; i++)
		{
			scanf("%d",&arr[i]);
			res = max(res,arr[i]);
		}
		//如果城市的数目 等于 邮箱的数目
		//就一个城市一个邮箱，直接输出最大的
		if (city == box)
		{
			printf("%d
",res);
			continue;
		}
		int l = 1,r = res;
		int flag, sum;
		while (l < r)
		{
			int mid = (l+r)>>1;
			if(check(mid))
				r=mid;
			else
				l=mid+1;
		}
		printf("%d
",r);
	}
	return 0;
}