poj 1064 cable master

http://poj.org/problem?id=1064

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
4 11
8.02
7.43
4.57
5.39

Sample Output
2.00

题目大意：输入n和k，n为提供的缆线条数，k为需要缆线的条数。接下来输入n个数字，分别为n条缆线的长度。求可以剪成k条缆线时每条缆线的最长长度。

题目类型：二分

思路：
二分长度，求出该程度下所能裁剪出的缆线条数。

错误点：
1.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).这个需要特判。
2.考虑生活常识，这个只能量到厘米，不能更加精确，所以其余的会被舍弃，在最后结果的时候不可以直接答案，答案是四舍五入后的结果，而这个需要去尾，所以int(right*100.0)/100.0。
3.有一组数据
1 10
100.00
answer：10.00
而我用left的时候取出来是9.99，所以就改了right
4.数据范围为1到10000，所以t可能用int会超，用long long.

#include<stdio.h>#include<iostream>#define N 10005#define eps 1e-5using namespace std;double a[N];int main(){    int n,k;    while(scanf("%d%d",&n,&k)!=EOF)    {        int i,t;        double sum=0;        for(i=0;i<n;i++)            {                scanf("%lf",&a[i]);                sum+=a[i];            }     if(double(0.01*k)>sum)            printf("0.00\n");     else          {            double left=0,right=(double)sum/(double)k,mid;            while(right-left>eps)            {                mid=(left+right)/2;               long long int t=0;                for(i=0;i<n;i++)                   t=t+int(a[i]/mid);                if(t>=k)                   left=mid;                else                   right=mid;            }            printf("%.2lf\n",int(right*100.0)/100.0);         }        }    return 0;}

这道题周赛时只有一个人做出来了，哈哈，这道题好流氓……

好喜欢叶子君