SCAU1255 Cable master 【待解决】

1255 Cable master

时间限制:1000MS  内存限制:10000K
提交次数:50 通过次数:4

题型: 外判编程题   语言: G++

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.

输入格式

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.

输出格式

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).

输入样例

4 118.027.434.575.39

输出样例

2.00

提示

 

来源

 Northeastern Europe 2001

题意：有n条不同长度的电缆，要分成k段长度相等的片段，求出分得电缆的最大可能长度。
解题思路：看到最大可能长度就知道这是一个二分查找的题目，就是用二分查找去查找最大可能长度。这题跟scau的10690那道题挺类似的。首先得到所有电缆里面最长的长度作为二分查找的右边界，以0为左边界（这里偷懒了hh，其实可以以所有电缆的总长度除以k作为左边界，因为每份都相等而且有k份），对于二分查找的每一个猜测值，用每一个电缆的长度除以它再取整再求和，得到mid长度下能得到的段数。如果段数大于k，说明分得太多，也就是太短，就让左边界等于mid，如果段数小于k，也就是太长，就让右边界等于mid，最后就能得出答案。

#include <iostream>#include <cstdio>using namespace std;int a[10010];int main(){int n,k,max=0;double temp;scanf("%d%d",&n,&k);for(int i=0;i<n;i++){scanf("%lf",&temp);a[i]=temp*100;if(max<a[i]) max=a[i]; //求最大长度}int l,r;l=0; //给左边界赋初始值0r=max; //给右边界赋初始值maxint cnt,mid = l+(r-l)/2;while(l<r){mid = l+(r-l)/2; //取中间值cnt=0;for(int i=0;i<n;i++){cnt+=(int)a[i]/mid; //求分成mid长度得到的段数}if(cnt<k) r=mid; else if(cnt>k) l=mid;else break;}double ans=mid*0.01;printf("%.2f",ans);return 0;}

不过我这代码在scauoj上运行时间是954ms！！！！虽然过了，但出题人完全可以多弄几个数据把我弄超时( •̀д•́)，poj上也有相同的题（poj1064）在poj上提交，直接就WA了QAQ，也不知道错在哪orz