Cable master（二分查找解）

原题链接
Cable master
Time Limit: 1000MS Memory Limit: 10000K
Total Submissions: 38336 Accepted: 8183
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
Source

Northeastern Europe 2001
原题的意思特别简单，就是说有N条绳子，每条绳子的长度不一，你可以切割绳子，但是你最后要得到k条绳子，问你能得到的绳子的最大的值是多少。这个时候就是要二分查找答案。

//http://poj.org/problem?id=1064#include <algorithm>#include <iostream>#include <utility>#include <sstream>#include <cstring>#include <cstdio>#include <vector>#include <queue>#include <stack>#include <cmath>#include <map>#include <set>using namespace std;typedef long long ll;const int MOD = int(1e9) + 7;//int MOD = 99990001;const int INF = 0x3f3f3f3f;const ll INFF = (~(0ULL)>>1);const double EPS = 1e-9;const double OO = 1e20;const double PI = acos(-1.0); //M_PI;const int fx[] = {-1, 1, 0, 0};const int fy[] = {0, 0, -1, 1};const int maxn=10000 + 5;int n,k;double L[maxn];//判断当前二分出来的这个答案是否满足要求bool can(double x){        int sum=0;        for(int i=0;i<n;i++)                sum+=(int)(L[i]/x);        return sum>=k;}//二分查找答案void solve(){        double l=0,r=INF;        for(int i=0;i<100;i++){//这里之所以循环100次是为了保证精度                double mid=(l+r)/2;                if(can(mid)) l=mid;                else r=mid;        }        printf("%.2f\n",floor(r*100)/100);//这里选择l或者是r都是符合题目要求的}int main(){        while(scanf("%d%d",&n,&k)==2){                for(int i=0;i<n;i++)                        scanf("%lf",&L[i]);                solve();        }        return 0;}