Hotel booking(spfa+floyd)

http://acm.hdu.edu.cn/showproblem.php?pid=2992

题意：有n个城市，编号为（1~n），有一些城市中有一些旅店，要求从一个城市到另一个城市不能超过10小时，问能否从1号城市到n号城市，如果能需要住的最少的旅店数目是多少。

思路：首先将1号城市和n号城市置为有旅店的城市，spfa求每个旅店到其它旅店的最短距离，如果距离小于10小时，将两个旅店之间的权值置为1，这样就能构造出所有旅店之间的图，然后对该图利用floyd求最短路。

#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <queue>
#include <vector>
const int N=10005;
const int INF=1<<28;
using namespace std;

struct node
{
    int v,w;
    node(int v,int w):v(v),w(w) {}
};
vector<node>vv[N];
int mp[120][120],id[N];
int a[N],dis[N];
bool vis[N];
int hotel,n;
void init()
{
    memset(id,0,sizeof(id));
    for (int i = 0; i <= hotel+2; i++)
    {
        for (int j = 0; j <= hotel+2; j++)
        {
            mp[i][j] = INF;
        }
        mp[i][i] = 0;
    }
    for (int i = 0; i <= n; i++)
        vv[i].clear();
}
void spfa(int s)
{
    queue<int>q;
    memset(vis,0,sizeof(vis));
    for (int i = 0; i <= n; i++)
        dis[i] = INF;
    dis[s] = 0;
    q.push(s);
    vis[s] = true;
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        vis[u] = false;
        for (int i = 0; i < (int)vv[u].size(); i++)
        {
            int v = vv[u][i].v;
            int w = vv[u][i].w;
            if(dis[v]>dis[u]+w)
            {
                dis[v] = dis[u]+w;
                if(!vis[v])
                {
                    q.push(v);
                    vis[v] = true;
                }
            }
        }
    }
    for (int i = 1; i <= n; i++)
    {
        if (dis[i]<=600)
            mp[id[s]][id[i]] = 1;
    }
}
void floyd()
{
    for (int k = 0; k <= hotel+1; k++)
    {
        for (int i = 0; i <= hotel+1; i++)
        {
            for (int j = 0; j <= hotel+1; j++)
                if(mp[i][j] > mp[i][k]+mp[k][j])
                    mp[i][j] = mp[i][k]+mp[k][j];
        }
    }
}
int main()
{
    while(scanf("%d",&n)&&n)
    {
        scanf("%d",&hotel);
        init();
        for (int i = 1; i <= hotel; i++)
        {
            scanf("%d",&a[i]);
            id[a[i]] = i;
        }
        a[0] = 1;
        a[hotel+1] = n;
        id[1] = 0;
        id[n] = hotel+1;
        int m,u,v,w;
        scanf("%d",&m);
        for (int i = 1; i <= m; i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            vv[u].push_back(node(v,w));
            vv[v].push_back(node(u,w));
        }
        for (int i = 0; i <= hotel; i++)
            spfa(a[i]);
        floyd();
        if (mp[0][hotel+1]>=INF)
            puts("-1");
        else
            printf("%d
",mp[0][hotel+1]-1);
    }
    return 0;
}