2 Construct Binary Tree Using Pre/In/Post Order traversal

Inorder和post Order来建树。

class Solution(object):
    def buildTree(self, inorder, postorder):
        """
        :type inorder: List[int]
        :type postorder: List[int]
        :rtype: TreeNode
        """
        if inorder:
            num = postorder.pop()
            root = TreeNode(num)
            index = inorder.index(num)
            root.right = self.buildTree(inorder[index+1:], postorder)
            root.left = self.buildTree(inorder[:index], postorder)
            return root

Pre Order和 In Order

# 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 inorder:
            num = preorder.pop(0)
            root = TreeNode(num)
            index = inorder.index(num)
            root.left = self.buildTree(preorder, inorder[:index])
            root.right = self.buildTree(preorder, inorder[index+1:])
            return root