【HDU】-1551-Cable master（二分）

Cable master

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 3677    Accepted Submission(s): 1416

Problem 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 input consists of several testcases. The first line of each testcase contains two integer numbers 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 centimeter and at most 100 kilometers in length. All lengths in the input are written with a centimeter precision, with exactly two digits after a decimal point.

The input is ended by line containing two 0's.

 

Output

For each testcase write to the output 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 must contain the single number "0.00" (without quotes).

 

Sample Input

4 118.027.434.575.390 0

 

Sample Output

2.00

 

二分的题目重点想判断条件，认真分析题意，知道对什么二分，逼近谁。

题解：分的越长数量越少，分得越短数量越多。使得数量非常逼近需求量就是可以求出分得最长的情况。

对长度二分，判断分的段数

#include<cstdio>#include<algorithm>using namespace std;double a[10010];int n,k;int dis(double x){int sum=0;for(int i=1;i<=n;i++){sum+=(int)(a[i]/x);if(sum>=k)//sum>=k时，已经是可能的情况退出，继续循环无意义还可能超时 break;}if(sum>=k)//sun<=k,分割太小，数量大，使mid变大，数量变小 return 1;elsereturn 0;}int main(){while(~scanf("%d %d",&n,&k)&&(n&&k)){for(int i=1;i<=n;i++)scanf("%lf",&a[i]);double l=0.0,r=100000.0;//最短0，最长100000 int size=50;while(size--){double mid=(l+r)/2;if(dis(mid))l=mid;elser=mid;}printf("%.2lf\n",l);}return 0;}