bzoj1674: [Usaco2005]Part Acquisition 裸dijkstra

#include <stdio.h>
#include <queue>
#include <string.h>
#include <algorithm>
#define inf 2000000000
using namespace std;
typedef pair<long long , int > pii;
priority_queue <pii, vector<pii>, greater<pii > > q;
struct node 
{
    int u, v, w, next;
}a[100005];
int tot, n, m, rxa, rxc, rya, ryc;
int dis[100005];
int rp, T, first[100005];
int done[100005];
void addedge(int st, int end, int val)
{
    a[++tot].u = st;a[tot].v = end;a[tot].w = val;
    a[tot].next =first[st];first[st] = tot;
}
int dij()
{
    for (int i = 1; i <= n; i++)dis[i] = inf;
    q.push(make_pair(0, 1));
    dis[1] = 0;
    while (!q.empty())
    {
        int u = q.top().second;q.pop();
        if(done[u])continue;
        done[u] = 1;
        for (int e = first[u]; e != -1; e = a[e].next)
        {
            int v = a[e].v;
            if (dis[u] + a[e].w < dis[v])
            {
                dis[v] = dis[u] + a[e].w;
                q.push(make_pair(dis[v], v));
            }
        }
    }
}
int main()
{
    scanf("%d %d", &m, &n);
    int x, y;
    memset(first, -1, sizeof(first));
     for (int i = 1; i <= m; i++)
     {
        scanf("%d %d", &x, &y);
        addedge(x, y, 1);
     }
     dij();
     if(dis[n] == inf)printf("-1\n");
     else  printf("%d\n", dis[n]+1);
     return 0;
}