Uva10986_sending email (Short Circuit)

Solution report

Ideas:

The shortest path.

#include <iostream>#include <cstring>#include <cstdio>#include <queue>#define inf 0x3f3f3f3f#define N 40000#define M 100000using 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<n;i++)    {        dis[i]=inf;        vis[i]=0;    }    dis[s]=0;    vis[s]=1;    queue<int >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<m;i++)        {            scanf("%d%d%d",&u,&v,&w);            add(u,v,w);            add(v,u,w);        }        spfa();        printf("Case #%d: ",k++);        if(dis[t]==inf)        printf("unreachable\n");        else printf("%d\n",dis[t]);    }    return 0;}

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 areNSMTP servers connected by network cables. Each ofMCables 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 serverSTo ServerTAlong 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.NTest Cases Follow. Each one starts with a line containingN(2 <=N<20000 ),M(0 <=M<50000 ),S(0 <=S<N) AndT(0 <=T<N).S! =T. The nextMLines 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 fromSToT. Print "unreachable" if there is no route fromSToT.

Sample Input	Sample output
32 1 0 10 1 1003 3 2 00 1 1000 2 2001 2 502 0 0 1	Case #1: 100Case #2: 150Case #3: unreachable

Problemsetter: Igor naverniouk

Uva10986_sending email (Short Circuit)