数学，需要细心

 I

Time limit: 5000MS    Memory limit: 32768K
Total Submit: 49    Accepted: 18

Program Source File: I.C, I.CPP

A  group  of  N Internet  Service  Provider  companies  (ISPs)  use  a  private communication channel that has

a maximum capacity of C traffic units per second. Each company transfers T traffic units per second through the

channel and gets a profit that is directly proportional to the  factor T(C - T N). The problem is to compute

T_optim, the smallest value of T that maximizes the total profit the N ISPs can get from using the channel.

Notice that N, C, T, and T_optim are integer numbers.

 

Write a program that reads sets of data from an input text file. Each data set corresponds  to  an  instance  of  the 

problem  above  and  contains  two  integral numbers –  N and C – with values in the range from 0 to 10^9.

The input data are separated by white spaces, are correct,  and terminate with an end of file. For each data set

the program computes the value of  T_optim according to the problem instance that corresponds to the data set.

The result is  printed on the standard output from the beginning of a line. There must be no empty

lines on the output. An example of input/output is shown below.

Input   
1 0
0 1
4 3
2 8
3 27
25 1000000000   
Output
0
0
0
2
4
20000000

 

注意可能会超出范围，所以用所得的结果减一下判断，还有就是注意不是单纯的求导得出来结果取整就好了，要在他附近几个值判断！

 

#include<iostream> using namespace std; int main() { double n,k; while(scanf("%lf%lf",&n,&k)!=EOF) { double t; if(n==0) { t=0; printf("0/n"); continue; } else t=k/2/n; t=(int)t; int t1=t-1,t2=t,t3=t+1,ans1,ans2,ans3; /*ans1=t1*(k-n*t1); ans2=t2*(k-n*t2); ans3=t3*(k-n*t3);*/ ans1=2*n*t-n-k; ans2=2*n*t-k+n; ans3=4*n*t-2*k; if(ans1>=0) { if(ans3>=0) t=t1; else t=t3; } else { if(ans2>=0) t=t2; else t=t3; } printf("%d/n",(int)t); } }