模板题目.
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:
def myBuildTree(preorder_left: int, preorder_right: int, inorder_left: int, inorder_right: int):
if preorder_left > preorder_right:
return None
preorder_root = preorder_left
inorder_root = index[preorder[preorder_root]]
root = TreeNode(preorder[preorder_root])
size_left_subtree = inorder_root - inorder_left
root.left = myBuildTree(preorder_left + 1, preorder_left + size_left_subtree, inorder_left, inorder_root - 1)
root.right = myBuildTree(preorder_left + size_left_subtree + 1, preorder_right, inorder_root + 1, inorder_right)
return root
n = len(preorder)
index = {element: i for i, element in enumerate(inorder)}
return myBuildTree(0, n - 1, 0, n - 1)