UVa10986_Sending email(最短路)(小白书图论专题)

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;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(2nm (0mS (0Sn) and T (0Tn). 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 (0w

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

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分类:默认分类 时间:2015-02-27 人气:4
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