UVa10986_Sending email(最短路)(小白書圖論專題)
解題報告
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;iQ;
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
