Zadanie z grafem - Python iteracyjnie

n = int(input())

graf = [[] for _ in range(n)]
distances = [[0 for _ in range(n)] for _ in range(n)]
visited = [False for _ in range(n)]
maximum = 0
parents = [-1 for _ in range(n)]

for _ in range(n-1):
    a, b = map(int, input().split())
    graf[a-1].append(b-1)
    graf[b-1].append(a-1)


S = [0]

# DFS iteracyjnie
while S:
    v = S.pop()
    parent = parents[v]

    if parent != -1:
        for i in range(n):
            if visited[i]:
                distances[i][v] = distances[i][parent] + 1
                distances[v][i] = distances[parent][i] + 1

                if distances[v][i] > maximum:
                    maximum = distances[v][i]

    visited[v] = True
    for neighbor in graf[v]:
        if not visited[neighbor]:
            S.append(neighbor)
            parents[neighbor] = v


print(maximum)