[算法-二叉树前中后序遍历]

treenode_pre_in_post_solution.py

class TreeNode:
  def __init__(self, val):
    self.val = val
    self.left, self.right = None, None

# 二叉树前中后序遍历
class Solution:
    def __init__(self):
        self.traverse = []
    # 前序遍历组合
    def preorder(self, root):
          if root:
              self.traverse.append(root.val) 
              self.preorder(root.left)
              self.preorder(root.right)
          return self.traverse
    
    # 中序遍历组合
    def inorder(self, root):
          if root:
              self.inorder(root.left)
              self.traverse.append(root.val) 
              self.inorder(root.right)
          return self.traverse

    # 后序遍历组合
    def postorder(self, root):
        if root:
            self.postorder(root.left)
            self.postorder(root.right)
            self.traverse.append(root.val)
        return self.traverse

# 初始化构造二叉树
Tree = TreeNode(2)
Tree.left = TreeNode(1)
Tree.right = TreeNode(3)
Tree.right.left = TreeNode(7)
Tree.right.right = TreeNode(9)

# 执行不同类型的遍历并输出
solution = Solution()
prev = solution.preorder(Tree)  # [2, 1, 3, 7, 9] 
solution = Solution()
inor = solution.inorder(Tree)  # [1, 2, 7, 3, 9]
solution = Solution()
post = solution.postorder(Tree)  # [1, 7, 9, 3, 2]
print(prev, inor, post)