二、stl ，模拟，贪心等 [Cloned] D - stl 的 map

原题：

Once again, James Bond is fleeing from some evil people who want to see him dead. Fortunately, he has left a bungee rope on a nearby highway bridge which he can use to escape from his enemies. His plan is to attach one end of the rope to the bridge, the other end of the rope to his body and jump off the bridge. At the moment he reaches the ground, he will cut the rope, jump into his car and be gone. 

Unfortunately, he had not had enough time to calculate whether the bungee rope has the right length, so it is not clear at all what is going to happen when he jumps off the bridge. There are three possible scenarios: 

• The rope is too short (or too strong), and James Bond will never reach the ground. 
• The rope is too long (or too weak), and James Bond will be going too fast when he touches the ground. Even for a
• special agent, this can be very dangerous. You may assume that if he collides at a speed of more than 10 m/s, he will not survive the impact.

The rope's length and strength are good. James Bond touches the ground at a comfortable speed and can escape. 
As his employer, you would like to know whether James Bond survives or whether you should place a job ad for the soon-to-be vacant position in the local newspaper. Your physicists claim that: 

• The force with which James is pulled towards the earth is 
  9.81 * w, 
  where w is his weight in kilograms and 9.81 is the Earth acceleration in meters over squared seconds. 
• Mr. Bond falls freely until the rope tautens. Then the force with which the bungee rope pulls him back into the sky depends on the current length of the rope and is 
  k * Δl, 
  where Δl is the difference between the rope's current length and its nominal, unexpanded length, and k is a rope-specific constant.

Given the rope's strength k, the nominal length of the rope l in meters, the height of the bridge s in meters, and James Bond's body weight w, you have to determine what is going to happen to our hero. For all your calculations, you may assume that James Bond is a point at the end of the rope and the rope has no mass. You may further assume that k, l, s, and w are non-negative and that s < 200.

题意：

物理题啊喂！詹姆斯邦德从桥上跳下去，他身后拴着一根弹力绳，给出绳子长度，绳子劲度系数，桥高度，他的体重，重力加速度等量，问邦德落地时的速度是否超过10m/s（超过就死翘翘了）

题解：

不是很懂为啥这个题头是map，就是个物理题啊。就是能量守恒定律，先把各个点的能量算一下表示出来，然后根据功能关系算落地时候的速度（或者不能落地），然候不同情况输出不同就ok了。

代码：AC

#include <iostream>
#include <cmath>
using namespace std;
const double g=9.81;               
int main()
{
    double k,l,s,w;
    double E0,E1,E2,E4;
    while (cin>>k>>l>>s>>w)
    {
        if (k==0&&l==0&&s==0&&w==0)
            break;
        E0=0.5*k*(s-l)*(s-l);        
        E1=w*g*s;                     
        E2=0.5*w*10*10;                
        E4=E1-E0;                      
        if (l>s)
        {
            if (E1>E2)
                cout<<"Killed by the impact."<<endl;
            else
                cout<<"James Bond survives."<<endl;
        }
        else
        {
            if(E0>E1)
                cout<<"Stuck in the air."<<endl;
            else if(E4<E2)
                cout<<"James Bond survives."<<endl;
            else
                cout<<"Killed by the impact."<<endl;
        }
    }
    return 0;
}