BOJ - 1967 - 트리의 지름

import sys
from collections import deque

def BFS(graph, x, mode, N):
    Q = deque()
    Q.append(x)
    check = [-1 for _ in range(N)]
    check[x] = 0

    while Q:
        x = Q.popleft()

        for nx, weight in graph[x]:
            if check[nx] == -1:
                check[nx] = check[x] + weight
                Q.append(nx)
    if mode:
        return check.index(max(check))
    else:
        return max(check)


def solution():
    N = int(input())
    graph = [[] for _ in range(N)]
    for _ in range(N-1):
        x, y, w = map(int, sys.stdin.readline().split())
        graph[x-1].append((y-1, w))
        graph[y-1].append((x-1, w))
    print(BFS(graph, BFS(graph, 0, True, N), False, N))
solution()

https://www.acmicpc.net/problem/1967