POJ 2387 Til the Cows Come Home (单源最短路SPFA解法)

单源最短路问题，SPFA解法

//9050848 NKHelloWorld 2387 Accepted 272K 63MS C++ 1194B 2011-08-01 14:19:20
//9050982 NKHelloWorld 2387 Accepted 276K 63MS C++ 1559B 2011-08-01 14:30:19
//9050987 NKHelloWorld 2387 Accepted 680K 47MS G++ 1638B 2011-08-01 14:30:41
//1A µÚÒ»µÀSPFA
#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
typedef struct
{
    int to,dis;
}EDGE;
vector<EDGE> edge[1001];
queue<int> que;
bool inque[1001];
int dis[1001],n,t,cnt[1001];

int spfa(int start,int end)
{
    int i,a;
    memset(inque,false,sizeof(inque));
    memset(cnt,0,sizeof(cnt));
    for(i=1;i<=n;i++)
        dis[i] = 2147483647;
    dis[start] = 0;
    inque[start] = true;
    cnt[start] = 1;
    que.push(start);
    while(!que.empty())
    {
        a = que.front();
        que.pop();
        inque[a] = false;
        for(i=0;i<edge[a].size();i++)
        {
            if(dis[edge[a][i].to] - edge[a][i].dis > dis[a])
            {
                dis[edge[a][i].to] = dis[a] + edge[a][i].dis;
                if(! inque[edge[a][i].to])
                {
                    inque[edge[a][i].to] = true;
                    que.push(edge[a][i].to);
                    if(++cnt[edge[a][i].to] > n)
                    {
                        return -1;
                    }
                }
            }
        }
    }
    return dis[end];
}

int main()
{
    int i,j,a,b,d;
    EDGE tedge;
    scanf("%d%d",&t,&n);
    for(i=1;i<=t;i++)
    {
        scanf("%d%d%d",&a,&b,&d);
        tedge.to = b;   tedge.dis = d;  edge[a].push_back(tedge);
        tedge.to = a;   edge[b].push_back(tedge);
    }
    printf("%d\n",spfa(1,n));

    return 0;
}