POJ 1064 Cable master [二分]

Cable master

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 70874		Accepted: 14445

Description

Inhabitants of the Wonderland have decided to hold a regional programming contest. The Judging Committee has volunteered and has promised to organize the most honest contest ever. It was decided to connect computers for the contestants using a "star" topology - i.e. connect them all to a single central hub. To organize a truly honest contest, the Head of the Judging Committee has decreed to place all contestants evenly around the hub on an equal distance from it.
To buy network cables, the Judging Committee has contacted a local network solutions provider with a request to sell for them a specified number of cables with equal lengths. The Judging Committee wants the cables to be as long as possible to sit contestants as far from each other as possible.
The Cable Master of the company was assigned to the task. He knows the length of each cable in the stock up to a centimeter,and he can cut them with a centimeter precision being told the length of the pieces he must cut. However, this time, the length is not known and the Cable Master is completely puzzled.
You are to help the Cable Master, by writing a program that will determine the maximal possible length of a cable piece that can be cut from the cables in the stock, to get the specified number of pieces.

Input

The first line of the input file contains two integer numb ers N and K, separated by a space. N (1 = N = 10000) is the number of cables in the stock, and K (1 = K = 10000) is the number of requested pieces. The first line is followed by N lines with one number per line, that specify the length of each cable in the stock in meters. All cables are at least 1 meter and at most 100 kilometers in length. All lengths in the input file are written with a centimeter precision, with exactly two digits after a decimal point.

Output

Write to the output file the maximal length (in meters) of the pieces that Cable Master may cut from the cables in the stock to get the requested number of pieces. The number must be written with a centimeter precision, with exactly two digits after a decimal point.
If it is not possible to cut the requested number of pieces each one being at least one centimeter long, then the output file must contain the single number "0.00" (without quotes).

Sample Input

Sample Output

2.00

思路:很简单的题目，但一直WA。

题目有几个坑点。首先是精度问题，用double。其次是小数二分用小于一个非常小的数来判断，但是这道题不知道为什么不行，只有用for循环才过（可能还是精度问题）。最后输出的时候要向下取整，举个例子：如果计算出来的2.348符合输出的时候会四舍五入输出2.35就不符合了只能向下取2.34

代码中有注解。

#include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
int main()
{
    int n,k;
    while(scanf("%d %d",&n,&k)!=EOF)
    {
        double s[100010];
        for(int i=0; i<n; i++)
        {
            cin>>s[i];
        }
        double left=0;//相当于无穷小
        double right=100000;//相当于无穷大
        double mid;
        for(int i=0;i<100;i++)
        {
            mid=(left+right)/2;
            int cnt=0;
            for(int i=0; i<n; i++)
            {
                cnt+=(int)(s[i]/mid);
            }
            if(cnt<k)
                right=mid;
            else
                left=mid;
        }
        /*floor为向下取整 如果计算出来的2.348符合，
        输出的时候会四舍五入输出2.35就不符合了
        只能先乘以100为234.8在向下取整取234在除以100*/
        printf("%.2lf
",floor(left*100)/100);
    }
}