递归与二叉树_中序和后序重建二叉树

# coding: utf-8
'''
题目：输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。
假设输入的前序遍历和中序遍历的结果中都不含重复的数字。
'''
class Node:
  def __init__(self, data, left, right):
    self.data = data
    self.left = left
    self.right = right


def construct_tree(pre_order, mid_order):
  # 忽略参数合法性判断
  if len(pre_order) == 0 :
    return None
  # 前序遍历的第一个结点一定是根结点
  root_data = pre_order[0]
  for i in range(0, len(mid_order)):
    if mid_order[i] == root_data:
      break
  # 递归构造左子树和右子树
  left = construct_tree(pre_order[1 : 1 + i], mid_order[:i])
  right = construct_tree(pre_order[1 + i:], mid_order[i+1:])

  return Node(root_data, left, right)


if __name__ == '__main__':
  pre_order = [1, 2, 4, 7, 3, 5, 6, 8]
  mid_order = [4, 7, 2, 1, 5, 3, 8, 6]
  root = construct_tree(pre_order, mid_order)
  print root.data
  print root.left.data
  print root.right.data
  print root.left.left.data
  print root.left.left.right.data
  print root.right.right.left
  print root.right.left.data