二叉树算法:已知前序遍历和中序遍历求二叉树代码,用python实现:
# -------------------------------------------------------------------------------
# coding:utf-8
# Description:
# Reference:
# Author: dacongming
# Date: 2023/7/10
# -------------------------------------------------------------------------------
class TreeNode:
def __init__(self,val = 0,left = None, right = None):
self.val = val
self.left = left
self.right = right
def buildTree(preorder, inorder):
if not preorder or not inorder:
return None
root_val = preorder[0]
root = TreeNode(root_val)
root_index = inorder.index(root_val)
left_inorder = inorder[:root_index]
right_inorder = inorder[root_index+1:]
left_preorder = preorder[1:1+len(left_inorder)]
right_preorder = preorder[1+len(left_inorder):]
root.left = buildTree(left_preorder, left_inorder)
root.right = buildTree(right_preorder, right_inorder)
return root
preorder = [3, 9, 20, 15, 7]
inorder = [9, 3, 15, 20, 7]
root = buildTree(preorder, inorder)
测试代码:
# 验证结果
def inorderTraversal(root):
if not root:
return []
result = []
stack = []
curr = root
while curr or stack:
while curr:
stack.append(curr)
curr = curr.left
curr = stack.pop()
result.append(curr.val)
curr = curr.right
return result
print(inorderTraversal(root)) # 输出 [9, 3, 15, 20, 7]