给出一个先序序列与后序序列相同的二叉树

一个先序序列与后序序列相同的二叉树可以是一个只有一个节点的二叉树，该节点既是根节点也是叶子节点。具体实现如下：

class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

class Solution:
    def constructTree(self, preorder):
        if not preorder:
            return None
        root = TreeNode(preorder[0])
        return root

    def preorderTraversal(self, root):
        if not root:
            return []
        res = []
        res.append(root.val)
        res += self.preorderTraversal(root.left)
        res += self.preorderTraversal(root.right)
        return res

    def inorderTraversal(self, root):
        if not root:
            return []
        res = []
        res += self.inorderTraversal(root.left)
        res.append(root.val)
        res += self.inorderTraversal(root.right)
        return res

    def postorderTraversal(self, root):
        if not root:
            return []
        res = []
        res += self.postorderTraversal(root.left)
        res += self.postorderTraversal(root.right)
        res.append(root.val)
        return res

    def countLeaves(self, root):
        if not root:
            return 0
        if not root.left and not root.right:
            return 1
        return self.countLeaves(root.left) + self.countLeaves(root.right)

preorder = [1]
solution = Solution()
root = solution.constructTree(preorder)
print("先序遍历序列：", solution.preorderTraversal(root))
print("中序遍历序列：", solution.inorderTraversal(root))
print("后序遍历序列：", solution.postorderTraversal(root))
print("叶子数：", solution.countLeaves(root))