180131_2644_촌수계산

//https://www.acmicpc.net/problem/2644 #include <iostream>

#include <queue>

#include <cstring>

using namespace std;

int parent[101]; // parent[i] :: i의 부모

int chon[101];

int n;

void bfs(int start)

{

queue<int> q;

q.push(start);

chon[start]=0;

while(!q.empty())

{

int now=q.front();

q.pop();

for(int i=1; i<=n; i++){

if(parent[i]==now && chon[i] ==-1){

q.push(i);

chon[i]=chon[now]+1;

}

}

if(parent[now]!=0 && chon[parent[now]] ==-1)

{q.push(parent[now]); chon[parent[now]]=chon[now]+1;}

}

}

int main()

{

int a, b, m;

cin >> n >> a >> b >> m;

for(int i=0; i<m; i++){

int x, y;

cin >> x >> y;

parent[y]=x;//y의 부모가 x

}

memset(chon, -1, sizeof(chon));

bfs(a);

cout << chon[b];

}