촌수계산

설계도

코드

from collections import deque
def draw(n,m):
    graph = [[]*(n+1) for _ in range(n+1)]
    for i in range(m):
        a,b = map(int,input().split())
        graph[a].append(b)
        graph[b].append(a)
    return graph
def bfs(n,target1,target2,graph):
    q = deque([(target1,0)])
    visited = [False]*(n+1)
    visited[target1] = True

    while q:
        cur, chonsu = q.popleft()
        if cur == target2:
            return chonsu
        for next in graph[cur]:
            if not visited[next]:
                q.append((next,chonsu+1))
                visited[cur] = True
    chonsu = -1
    return chonsu

n = int(input())
target1,target2 = map(int,input().split())
m = int(input())
graph = draw(n,m)
chonsu = bfs(n,target1,target2,graph)
print(chonsu)