처음에 lca인가 봤더니 그냥 BFS. 이진트리라면 lca써야했을지도. import sys input = sys.stdin.readline from collections import deque def bfs(start,target): visited = {i: 0 for i in range(n+1)} visited[start] = 1 q = deque() q.append(start) while q: cur_node = q.popleft() if cur_node==target: return visited[cur_node] -1 for next_node in graph[cur_node]: if not visited[next_node]: visited[next_node] = visited[cur_node] + ..