分治法

Python 代码

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution(object):
    def buildTree(self, preorder, inorder):
        """
        :type preorder: List[int]
        :type inorder: List[int]
        :rtype: TreeNode
        """
        if not preorder:
            return None
        for i in range(len(inorder)):
            if inorder[i] == preorder[0]:
                inorder_left = inorder[:i]
                inorder_right = inorder[i + 1 : ]
                preorder_left = preorder[1 : len(inorder_left) + 1]
                preorder_right = preorder[len(inorder_left) + 1 :]
                root = TreeNode(preorder[0])
                root.left = self.buildTree(preorder_left, inorder_left)
                root.right = self.buildTree(preorder_right, inorder_right)
                return root