[백준,PS,BFS][PYTHON] #2644 . 촌수계산

https://www.acmicpc.net/problem/2644

from collections import deque
def bfs(x):
    global count
    q.append(start)
    visited[start] =1
    count[start] = 1
    while q:
        x = q.popleft()
        
        for i in range(len(graph[x])):
            nx = graph[x][i]
            if visited[nx] != 1:
             
                visited[nx] = 1
                q.append(nx)
                count[nx] = count[x] +1 #key _point 부분
 ################main#############               
vertex = int(input())
start,end = map(int,input().split())
edge =int(input())
graph =[  []  for _ in range(vertex+1)]
visited = [ 0 for _ in range(vertex+1)]
count =  [ 0 for _ in range(vertex+1)] # 촌수를 계산할수있는 같은이중 리스트를 만들어주는것

q = deque()

for _ in range(edge):
    x,y = map(int,input().split())
    graph[x].append(y)
    graph[y].append(x)

bfs(start)

#print(graph)
#print(count)
#print(visited)
print(count[end] - count[start])