链接：http://www.rqnoj.cn/problem/86
思路：单源点最短路
建图：首先根据父子关系连双向边，边权是距离/速度；再根据跳跃关系连单向边，边权是自由落体的时间（注意自由下落是一个匀加速过程，若中途停下再跳一定没有直接跳优）。
我的实现：
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <cmath> 5 #include <algorithm> 6 #include <queue> 7 using namespace std; 8 #define MaxN 120 9 #define MaxM 320 10 #define INF 100000 11 struct P 12 { 13 int v,x,y; 14 }Point[MaxN]; 15 struct node 16 { 17 int v; 18 double dist; 19 node *next; 20 }; 21 node Edge[MaxM]; 22 node *cnt=&Edge[0]; 23 node *adj[MaxN]; 24 double Dist[MaxN]; 25 int N,V; 26 inline void Get_int(int &Ret) 27 { 28 char ch; 29 bool flag=false; 30 for(;ch=getchar(),ch<'0'||ch>'9';) 31 if(ch=='-') 32 flag=true; 33 for(Ret=ch-'0';ch=getchar(),ch>='0'&&ch<='9';Ret=Ret*10+ch-'0'); 34 flag&&(Ret=-Ret); 35 } 36 inline double Dis(int a,int b) 37 { 38 double dx=(double)(Point[a].x-Point[b].x); 39 double dy=(double)(Point[a].y-Point[b].y); 40 return sqrt(dx*dx+dy*dy); 41 } 42 inline void Addedge(int u,int v,double w) 43 { 44 node *p=++cnt; 45 p->v=v; 46 p->dist=w; 47 p->next=adj[u]; 48 adj[u]=p; 49 } 50 bool Cmp(P a,P b) 51 { 52 return ((a.x<b.x)||(a.x==b.x&&a.y<b.y)); 53 } 54 inline void Read_Build() 55 { 56 Get_int(N); Get_int(V); 57 int i,j,pos,fa; 58 double T; 59 for(i=1;i<=N;++i) 60 { 61 Get_int(Point[i].x);Get_int(Point[i].y); 62 Point[i].v=i; 63 Get_int(fa); 64 if(!fa) continue; 65 T=Dis(i,fa)/(double)V; 66 Addedge(i,fa,T); Addedge(fa,i,T); 67 } 68 sort(Point+1,Point+N+1,Cmp); 69 for(i=2;i<=N;i++) 70 { 71 if(Point[i].x!=Point[i-1].x) 72 { 73 pos=i; 74 } 75 else 76 { 77 for(j=pos;j<i;j++) 78 { 79 T=sqrt((double)(Point[i].y-Point[j].y)/5.0); 80 Addedge(Point[i].v,Point[j].v,T); 81 } 82 } 83 84 } 85 } 86 struct cmp 87 { 88 bool operator()(node a,node b) 89 { 90 return a.dist>b.dist; 91 } 92 }; 93 priority_queue <node, vector<node>, cmp> q; 94 void Dijkstra(int s) 95 { 96 node c,d,*p; 97 int u,v; 98 for(int i=1;i<=N;i++) 99 Dist[i]=INF; 100 Dist[s]=0; 101 c.v=s;c.dist=0; 102 q.push(c); 103 while(!q.empty()) 104 { 105 d=q.top();q.pop(); 106 u=d.v; 107 for(p=adj[u];p!=NULL;p=p->next) 108 { 109 v=p->v; 110 if(Dist[v]>Dist[u]+p->dist) 111 { 112 Dist[v]=Dist[u]+p->dist; 113 d.v=v;d.dist=Dist[v]; 114 q.push(d); 115 } 116 } 117 } 118 } 119 int main() 120 { 121 Read_Build(); 122 Dijkstra(1); 123 printf("%.2lf ",Dist[N]); 124 return 0; 125 }