LeetCode105 从前序与中序遍历序列构造二叉树

LeetCode105 从前序与中序遍历序列构造二叉树

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)