Problem Challenge 2: Minimum Height Trees (hard)

from collections import deque

class Solution:

  # build a unidrictional graph 
  def build_graph(self, nodes, edges):
    graph, indegree = {}, {}
    for i in range(nodes):
      graph[i] = []
      indegree[i] = 0 
    for node1, node2 in edges:
      graph[node1].append(node2)
      graph[node2].append(node1)
      indegree[node1] += 1
      indegree[node2] += 1
    return(graph, indegree)
   
  def findTrees(self, nodes, edges):
    if nodes == 1:
      return [0]

    graph, indegree = self.build_graph(nodes, edges)
    q = deque([x for x in indegree if indegree[x] == 1])

    result = []
    
    # topological ordering can be done on unidirectional graph too
    # for that we should do indegree[neighbor] == 1 as edge nodes are linked
    # topological finds the center