POJ 1847

熟悉下最短路问题，用dijkstra a了，不过一定一定要注意审题

#include <iostream>
#include <algorithm>
#include <queue>
#include <string>
#include <vector>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <string>
#include <stack>
#include <map>
#include <set>
#include <deque>
using namespace std;

const int maxn= 105;
const int INF= 0x3f3f3f3f;

struct Edge
{
	int v, c;
	Edge(int _v= 0, int _c= 0) : v(_v), c(_c) {}
};
struct HeapNode
{
	int u, c;
	HeapNode(int _u= 0, int _c= 0) : u(_u), c(_c) {}
	bool operator < (const HeapNode &rhs) const
	{
		return c> rhs.c;
	}
};
vector<Edge> G[maxn];
bool vis[maxn];
int dis[maxn];

void Dijkstra(int n, int s)
{
	priority_queue<HeapNode> Q;
	HeapNode cur;
	for (int i= 1; i<= n; ++i){
		dis[i]= INF;
	}
	memset(vis, 0, sizeof(vis));
	dis[s]= 0;
	Q.push(HeapNode(s, 0));
	int u, v;

	while (!Q.empty()){
		cur= Q.top();
		Q.pop();
		if (vis[cur.u]){
			continue;
		}

		u= cur.u;
		vis[u]= 1;
		int sz= G[u].size();
		for (int i= 0; i< sz; ++i){
			v= G[u][i].v;
			if (!vis[v] && dis[v]> dis[u]+G[u][i].c){
				dis[v]= dis[u]+G[u][i].c;
				Q.push(HeapNode(v, dis[v]));
			}
		}
	}
}

int main(int argc, char const *argv[])
{
	int n, a, b;
	scanf("%d %d %d", &n, &a, &b);

	for (int i= 1; i<= n; ++i){
		int k, v;
		scanf("%d", &k);
		for (int j= 0; j< k; ++j){
			scanf("%d", &v);
			G[i].push_back(Edge(v, 0== j ? 0 : 1));
		}
	}
	Dijkstra(n, a);
	printf("%d\n", dis[b]< INF ? dis[b] : -1);

	return 0;
}