LeetCode Construct Binary Tree from Inorder and Postorder Traversal

LeetCode解题之Construct Binary Tree from Inorder and Postorder Traversal

原题

通过一棵二叉树的中序和后序排列来得出它的树形结构。

注意点：

• 无

例子:

输入: inorder = [9,3,14,15,20,7], postorder = [9,14,15,7,20,3]

输出:

    3
   / \   9  20
    /  \    15   7
  /
 14

解题思路

1. 因为后序中的节点为根节点,所以取出后序的最后一个节点
2. 用后序的最后一个节点可以将中序分成左右子树，然后取出后序的倒数第二个节点将左右子树再次划分
3. 当将中序全部划分为单个点时就结束

AC源码

# 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, inorder, postorder):
        """ :type inorder: List[int] :type postorder: List[int] :rtype: TreeNode """
        self.postorder = postorder
        self.inorder = inorder
        return self._buildTree(0, len(inorder))

    def _buildTree(self, start, end):
        if start < end:
            root = TreeNode(self.postorder.pop())
            index = self.inorder.index(root.val)
            root.right = self._buildTree(index + 1, end)
            root.left = self._buildTree(start, index)
            return root


if __name__ == "__main__":
    None

欢迎查看我的Github (https://github.com/gavinfish/LeetCode-Python) 来获得相关源码。