UVa 10986

链接：http://uva.onlinejudge.org/index.php?

option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=1927

//邻接表+队列

#include <iostream>
#include <string.h>
#include <queue>
#include <stdio.h>
using namespace std;
#define edge_max 100005
#define vertex_max 100005
const int inf = (1<<20);
struct Node
{
    int u,w;
    int next;
}Edge[edge_max];

int pre[vertex_max],dist[vertex_max]; //以p[i]的i为起点储存的边数序号
int n,m,start,stop; //顶点数，边数 起点，终点
bool vis[vertex_max]; //记录
void init()
{
    memset(pre,-1,sizeof(pre));
    int index=1;
    int v,u,w;
    for(int i=0;i<m;i++)
    {
        scanf("%d%d%d",&v,&u,&w);
        Edge[index].u=u;
        Edge[index].w=w;
        Edge[index].next=pre[v];
        pre[v]=index++;
        swap(v,u);
        Edge[index].u=u;
        Edge[index].w=w;
        Edge[index].next=pre[v];
        pre[v]=index++;
    }
}

void spfa(int v)
{
    queue <int> q;
    fill(dist,dist+n,inf);
    memset(vis,0,sizeof(vis));
    dist[v]=0;
    vis[v]=1;
    while(!q.empty())
        q.pop();
    q.push(v);
    while(!q.empty())
    {
        int top=q.front();
        q.pop();
        vis[top]=0;
        for(int i=pre[top];i!=-1;i=Edge[i].next)
        {
            int e=Edge[i].u;
            if(dist[e]>dist[top]+Edge[i].w)
            {
                dist[e]=dist[top]+Edge[i].w;
                if(!vis[e])
                {
                    q.push(e);
                    vis[e]=1;
                }
            }
        }
    }
}

int main()
{
    int t,cnt=1;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d%d%d",&n,&m,&start,&stop);
        init();
        spfa(start);
        printf("Case #%d: ",cnt++);
        if(dist[stop]!=inf)
            printf("%d
",dist[stop]);
        else
            printf("unreachable
");
    }
    return 0;
}