Cable master

本文介绍了一个关于电缆切割的问题,旨在帮助CableMaster确定如何从现有库存中切割出尽可能长且数量足够的电缆段,以满足一场编程比赛的需求。文章提供了一种通过二分查找算法来解决该问题的方法。

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Cable master

成绩10开启时间2018年02月11日 星期日 15:00
折扣0.8折扣时间2018年12月30日 星期日 18:00
允许迟交关闭时间2018年12月30日 星期日 20:00

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


二分答案。开始l=0,r=(所有之和)/k

因为精度的问题,直接选择了二分100次。

输出的时候加上floor函数,向下取整

#include<cstdio>
#include<algorithm>
#include<string>
#include<cmath>
using namespace std;
#define INF 100005
#define exp 1e-5
#define maxn 10005
double a[maxn];             //存电缆的长度
int n, need;
int check(double x)
{
	int unit = 0;
	for (int i = 0; i < n; i++)
		unit += (int)(a[i] / x);
	if (unit >= need)
		return 1;
	else
		return 0;
}
int main()
{
	freopen("1.txt", "r", stdin);

	while (scanf("%d %d", &n, &need) != EOF)
	{

		if (n == 0 && need == 0)
			return 0;
		double sum = 0;
		for (int i = 0; i < n; i++)
		{
			scanf("%lf", &a[i]);
			sum += a[i];
		}
		double lb = 0, ub = INF;
		for (int i = 0; i<100; i++)  //限定次数吧,别eps了,orz
		{
			double mid = (lb + ub) / 2;
			if (check(mid))
				lb = mid;
			else
				ub = mid;
		}

		printf("%.2f\n", floor(ub * 100) / 100);
	}

	return 0;
}

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