1 #include <stdio.h> 2 #include <queue> 3 #include <string.h> 4 #include <algorithm> 5 #define inf 2000000000 6 using namespace std; 7 typedef pair<long long , int > pii; 8 priority_queue <pii, vector<pii>, greater<pii > > q; 9 struct node 10 { 11 int u, v, w, next; 12 }a[100005]; 13 int tot, n, m, rxa, rxc, rya, ryc; 14 int dis[100005]; 15 int rp, T, first[100005]; 16 int done[100005]; 17 void addedge(int st, int end, int val) 18 { 19 a[++tot].u = st;a[tot].v = end;a[tot].w = val; 20 a[tot].next =first[st];first[st] = tot; 21 } 22 int dij() 23 { 24 for (int i = 1; i <= n; i++)dis[i] = inf; 25 q.push(make_pair(0, 1)); 26 dis[1] = 0; 27 while (!q.empty()) 28 { 29 int u = q.top().second;q.pop(); 30 if(done[u])continue; 31 done[u] = 1; 32 for (int e = first[u]; e != -1; e = a[e].next) 33 { 34 int v = a[e].v; 35 if (dis[u] + a[e].w < dis[v]) 36 { 37 dis[v] = dis[u] + a[e].w; 38 q.push(make_pair(dis[v], v)); 39 } 40 } 41 } 42 } 43 int main() 44 { 45 scanf("%d %d", &m, &n); 46 int x, y; 47 memset(first, -1, sizeof(first)); 48 for (int i = 1; i <= m; i++) 49 { 50 scanf("%d %d", &x, &y); 51 addedge(x, y, 1); 52 } 53 dij(); 54 if(dis[n] == inf)printf("-1 "); 55 else printf("%d ", dis[n]+1); 56 return 0; 57 }