解题报告

思路：

裸裸的最短路。

#include 
  
   
#include 
   
     #include 
    
      #include 
     
       #define inf 0x3f3f3f3f #define N 40000 #define M 100000 using namespace std; struct node { int v,w,next; }edge[M]; int head[N],dis[N],vis[N],cnt,n,m,s,t; void add(int u,int v,int w) { edge[cnt].v=v; edge[cnt].w=w; edge[cnt].next=head[u]; head[u]=cnt++; } void spfa() { for(int i=0;i
      
       Q; Q.push(s); while(!Q.empty()){ int u=Q.front(); Q.pop(); vis[u]=0; for(int i=head[u];i!=-1;i=edge[i].next) { int v=edge[i].v; if(dis[v]>dis[u]+edge[i].w) { dis[v]=dis[u]+edge[i].w; if(!vis[v]) { vis[v]=1; Q.push(v); } } } } } int main() { int i,j,T,u,v,w,k=1; scanf("%d",&T); while(T--) { memset(head,-1,sizeof(head)); cnt=0; scanf("%d%d%d%d",&n,&m,&s,&t); for(i=0;i
       
        
 
        
 
        
         Problem E
         
 
         Sending email
         
 Time Limit: 3 seconds
         
        
 
        
 
        
 
         
 
          
 
           
"A new internet watchdog is creating a stir in
 Springfield. Mr. X, if that is his real name, has
 come up with a sensational scoop."
 
          
 
         
 
        
 
        
Kent Brockman
 
        
There are n SMTP servers connected by network cables. Each of the m cables connects two computers and has a certain latency measured in milliseconds required to send an email message. What is the shortest time required to send a message from server S to server T along a sequence of cables? Assume that there is no delay incurred at any of the servers.
 
        
Input
 The first line of input gives the number of cases, N. N test cases follow. Each one starts with a line containing n(2<=n<20000), m (0<=m<50000), S (0<=S<n) and T (0<=T<n). S!=T. The next m lines will each contain 3 integers: 2 different servers (in the range [0, n-1]) that are connected by a bidirectional cable and the latency, w, along this cable (0<=w<=10000).
 
        
Output
 For each test case, output the line "Case #x:" followed by the number of milliseconds required to send a message from S toT. Print "unreachable" if there is no route from S to T.
 
        
 
         
 
          
 
           
Sample Input
 
           
Sample Output
 
          
 
          
 
           
 
3
2 1 0 1
0 1 100
3 3 2 0
0 1 100
0 2 200
1 2 50
2 0 0 1
 
 
           
 
Case #1: 100
Case #2: 150
Case #3: unreachable
 
 
          
 
         
 
        
 
        
 
        
 Problemsetter: Igor Naverniouk