开车旅行

题解：
遍历起点就OK

#include<bits/stdc++.h>
#define ll long long
#define inf 10000000000
using namespace std;
ll n;
ll X;
ll H[100010];
ll wheA[100010][2];
ll wheB[100010][2];
ll s,m;
long double ans1=inf;
ll read(){
   ll num=0,f=1;
   char ch;
   ch=getchar();
   while(ch>'9'||ch<'0'){
   	if(ch=='-') f=-1;
   	ch=getchar();
   }
   while(ch<='9'&&ch>='0'){
   	num=(num<<3)+(num<<1)+ch-'0';
   	ch=getchar();
   }
   return f*num;
}
long double dfs(ll S,ll x,bool who,ll AS,ll BS){
//	if(AS+BS>S) return inf;
   if(x>=n){
   	if(BS==0){
   		return inf;
   	}
   	return (long double)AS/(long double)BS;
   }
   if(!who){
   	if(AS+wheA[x][1]+BS<=S){
   		return dfs(S,wheA[x][0],1,AS+wheA[x][1],BS);
   	}
   }
   else {
   	if(AS+wheB[x][1]+BS<=S){
   		return dfs(S,wheB[x][0],0,AS,BS+wheB[x][1]);
   	}
   }
   if(BS==0){
   	return inf;
   }
   return (long double)AS/(long double)BS;
}
void dfs_(ll S,ll x,bool who,ll AS,ll BS){
   if(x>=n){
   	printf("%lld %lld\n",AS,BS);
   	return;
   }
   if(!who){
   	if(AS+wheA[x][1]+BS<=S){
   		dfs_(S,wheA[x][0],1,AS+wheA[x][1],BS);
   		return;
   	}
   }
   else {
   	if(AS+wheB[x][1]+BS<=S){
   		dfs_(S,wheB[x][0],0,AS,BS+wheB[x][1]);
   	 	return;
   	}
   }
   printf("%lld %lld\n",AS,BS);
}
int main(){
   n=read();
   for(ll i=1;i<=n;i++){
   	H[i]=read();
   }
   H[n+1]=inf;
   for(ll i=1;i<=n-1;i++){
   	ll x=i+1;
   	ll y=i+2;
   	ll t;
   	if((abs(H[x]-H[i])>abs(H[y]-H[i]))||(((abs(H[x]-H[i])==abs(H[y]-H[i])))&&(H[y]-H[i]<0))) 
   		swap(x,y);
   	for(ll j=i+3;j<=n;j++){
   		if((abs(H[x]-H[i])>abs(H[j]-H[i]))||(((abs(H[x]-H[i])==abs(H[j]-H[i])))&&(H[j]-H[i]<0))){
   			t=x;
   			x=j;
   			y=t;
   			continue;
   		}
   		if(((abs(H[x]-H[i])<abs(H[j]-H[i]))&&(abs(H[j]-H[i])<abs(H[y]-H[i])))||((abs(H[j]-H[i])==abs(H[y]-H[i]))&&(H[j]-H[i]<0))){
   			y=j;
   			continue;
   		}
   	}
   	wheA[i][0]=y;
   	wheA[i][1]=abs(H[y]-H[i]);
   	wheB[i][0]=x;
   	wheB[i][1]=abs(H[x]-H[i]);
   }
   X=read();
   for(ll i=1;i<n;i++){
   	long double w=dfs(X,i,0,0,0);
   	if(ans1>w||(ans1==w&&H[i]>H[s])){
   		ans1=w;
   		s=i;
   	}
   }
   printf("%lld\n",s);
   m=read();
   while(m--){
   	int a,b;
   	a=read();
   	b=read();
   	dfs_(b,a,0,0,0);
   }
}