105. 从前序与中序遍历序列构造二叉树

原题

https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/

思路

递归

复杂度

时间：O(n)
空间：O(n)

Python代码

# 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]) -> Optional[TreeNode]:
        if not preorder or not inorder:
            return None
        root = TreeNode(preorder[0])
        index = inorder.index(preorder[0])
        root.left = self.buildTree(preorder[1 : index + 1], inorder[:index])
        root.right = self.buildTree(preorder[index + 1 :], inorder[index + 1 :])
        return root

Go代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func buildTree(preorder []int, inorder []int) *TreeNode {
	if len(preorder) == 0 || len(inorder) == 0 {
		return nil
	}
	root := &TreeNode{Val: preorder[0]}
	index := slices.Index(inorder, preorder[0])
	root.Left = buildTree(preorder[1:index+1], inorder[:index])
	root.Right = buildTree(preorder[index+1:], inorder[index+1:])
	return root
}