题解

呵呵哈哈

#include <iostream>
#include <cstdio>
#include <memory.h>
#include <vector>
#include <queue>
using namespace std;
struct node{
	int val, step;
};
vector <int> v[1005];
bool vis[1005];
int n, m, x, y;
int bfs(){//广搜
	queue <node> q;
	q.push({x, 0});
	while(!q.empty()){
		node head = q.front();
		q.pop();
		if(head.val == y) return head.step;
		for(int i = 0; i < v[head.val].size(); i++){
			if(!vis[v[head.val][i]]){
				vis[v[head.val][i]] = 1;
				q.push({v[head.val][i], head.step + 1});
			}
		}
	}
	return -1;
}
int main(){
	cin >> n >> m;
	for(int i = 1; i <= m; i++){
		cin >> x >> y;
		v[x].push_back(y);
	}
	cin >> x >> y;
	vis[x] = 1;
	cout << bfs();

	return 0;
}