POJ 1064 Cable master | 二分+精度

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#define N 10010
using namespace std;
double L[N],l,r,mid;
long long n,k;
//yjjsb
bool check(double lim)
{
    int ret=0;
    for (int i=1;i<=n;i++)
	ret+=int(floor(L[i]/lim));
    return ret>=k;
}
int main()
{
    scanf("%lld%lld",&n,&k);
    for (int i=1;i<=n;i++)
	scanf("%lf",&L[i]),r+=2*L[i];
    for (int i=1;i<=100;i++)
    {
	mid=(l+r)/2;
	if (check(mid)) l=mid;
	else r=mid;
    }
    printf("%.2f",floor(r*100)/100);
    return 0;
}