codeforces 5D Follow Traffic Rules

简单数学题，注意分类讨论即可，把特殊情况考虑清楚。

#include<bits/stdc++.h>
using namespace std;  
int main(){
	double a,v,l,d,w;  
	cin>>a>>v>>l>>d>>w;   
	if(v<=w){
		double sp=sqrt(2*a*d);  
		if(sp<=v){
			double t1=sqrt(2*d/a);  
			double delta=sp*sp-2*a*(d-l);  
			double t2=(-sp+sqrt(delta))/a;  
			if(sp+t2*a<=v)  {
				cout<<fixed<<setprecision(10)<<t1+t2<<endl;  
			}else {
				double tp=(v-sp)/a;  
				cout<<fixed<<setprecision(10)<<t1+tp+(l-d-sp*tp-a/2*tp*tp)/v<<endl; 
			}  
		} else {
			double t1=v/a;  
			double dist=d-a*t1*t1/2;  
			t1+=dist/v;  
			cout<<fixed<<setprecision(10)<<t1+(l-d)/v<<endl;  
		}  
	} else {
		double sp=sqrt(2*a*d);  
		if(sp<=w){
			double t1=sqrt(2*d/a);  
			double delta=sp*sp-2*a*(d-l); 
			double t2=(-sp+sqrt(delta))/a; 
			if(sp+t2*a<=v) {
				cout<<fixed<<setprecision(10)<<t1+t2<<endl; 
			}else {
				double tp=(v-sp)/a;  
				cout<<fixed<<setprecision(10)<<t1+tp+(l-d-sp*tp-a/2*tp*tp)/v<<endl;  
			}   
		} else {
			double t1=w/a;  
			double dist=d-a*t1*t1/2; 
			double tt=sqrt( ( a*t1*t1+dist)/a); 
			if(tt*a<=v)      
				t1+=2*(tt-t1);  
			else {
				double nd=v/a;  
				double dt=a/2*nd*nd;  
				t1=nd+(nd-t1)+(d-dt-(dt-a/2*t1*t1))/v;  
			}   
			double delta=w*w-2*a*(d-l);  
			double t2=(-w+sqrt(delta))/a; 
			if(w+t2*a<=v){
				cout<<fixed<<setprecision(10)<<t1+t2<<endl;  
			}else {
				double tp=(v-w)/a;  
				cout<<fixed<<setprecision(10)<<t1+tp+(l-d-w*tp-a/2*tp*tp)/v<<endl;  
			}   
		}  
	}
	return 0;  
}