#include <iostream>
#include <stdio.h>
using namespace std;
const int MAXN = 1000;
const int inf = 0x3fffffff;
int rel[MAXN+10][MAXN+10];
int dist[MAXN+10];
int pre[MAXN+10];
bool visit[MAXN+10];
int ans[MAXN+10];
int cnt;
int m, n;
void dijkstra()
{
    for(int i = 1; i <= n; i++)
    {
        visit[i] = false;
        dist[i] = inf;
    }
    dist[1] = 0;
    for(int i = 1; i <= n; i++)
    {
        int mmin = inf;
        int pos;
        for(int j = 1; j <= n; j++)
        {
            if(!visit[j] && dist[j]<mmin)
            {
                mmin = dist[j];
                pos = j;
            }
        }
        visit[pos] = true;
        for(int j = 1; j <= n; j++)
        {
            if(!visit[j] && dist[j] > dist[pos]+rel[pos][j])
            {
                pre[j] = pos;
                dist[j] = dist[pos]+rel[pos][j];
            }
        }
    }
}
int main()
{
    //freopen("in.txt", "r", stdin);
    while(scanf("%d%d", &m, &n) != EOF)
    {
        cnt = 0;
        for(int i = 1; i <= n; i++)
        {
            for(int j = 1; j <= n; j++) rel[i][j] = inf;
        }
        for(int i = 1; i <= m; i++)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            rel[u][v] = 1;
        }
        dijkstra();
        if(dist[n] == inf) printf("-1\n");
        else
        {
             ans[cnt++] = n;
            int tmp = pre[n];
            while(tmp != 1)
            {
                ans[cnt++] = tmp;
                tmp = pre[tmp];
            }
            ans[cnt++] = 1;
            printf("%d\n", cnt);
            for(int i = cnt-1; i >= 0; i--) printf("%d\n", ans[i]);
        }
    }
    return 0;
}

• 有向边。。 (0) 104GOGO 2011-11-26 09:46:16