from heapq import *

class Solution:
  
  def dfs(self, node, max_heap):
    # if leaf node
    if node and not node.left and not node.right:
      return 1

    left = right = 0 

    if node.left:
      left = self.dfs(node.left, max_heap)
    
    if node.right:
      right = self.dfs(node.right, max_heap)

    # heap is used to push the path lengths = left length + right length + node length = '1'
    heappush(max_heap, -(left + right + 1))

    return max(left, right) + 1

  def findDiameter(self, root):
    max_heap = []
    self.dfs(root, max_heap)
    return -heappop(max_heap)