poj2457

最短路

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define maxm 50005
#define maxn 1005

struct Edge
{
    int v, next;
}edge[maxm * 2];

int n, m;
int head[maxn];
int ecount;
int from[maxn];
int q[maxn];
int stk[maxn];
bool vis[maxn];

void addedge(int a, int b)
{
    edge[ecount].v = b;
    edge[ecount].next = head[a];
    head[a] = ecount++;
}

void input()
{
    scanf("%d%d", &m, &n);
    ecount = 0;
    memset(head, -1, sizeof(head));
    for (int i = 0; i < m; i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        a--;
        b--;
        addedge(a, b);
    }
}

void bfs()
{
    memset(vis, 0, sizeof(vis));
    int front = 0;
    int rear = 0;
    q[rear++] = 0;
    vis[0] = true;
    while (front != rear)
    {
        int u = q[front++];
        for (int i = head[u]; i != -1; i = edge[i].next)
        {
            int v = edge[i].v;
            if (!vis[v])
            {
                from[v] = u;
                q[rear++] = v;
                vis[v] = true;
                if (v == n - 1)
                    return;
            }
        }
    }
}

void print()
{
    int a = n - 1;
    int top = 0;
    while (a != 0)
    {
        stk[top++] = a;
        a = from[a];
    }
    stk[top++] = 0;
    printf("%d\n", top);
    for (int i = top - 1; i >= 0; i--)
        printf("%d\n", stk[i] + 1);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    input();
    bfs();
    if (!vis[n - 1])
        printf("-1\n");
    else
        print();
    return 0;
}