2.编写非递归遍历算法,实现:给定一棵二叉树的先序通历序列和中序通历序列，创建这棵二叉树。 (1 输出二叉树的后序遍历的结点序列。 (2)输出二叉树的叶子结点。 (3)统计二叉树的结点个数。

1. 非递归遍历算法示例代码：

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

def buildTree(preorder, inorder):
    if not preorder or not inorder:
        return None
    
    root = TreeNode(preorder[0])
    stack = [root]
    inorderIndex = 0
    
    for i in range(1, len(preorder)):
        node = TreeNode(preorder[i])
        if node.val != stack[-1].val:
            stack[-1].left = node
        else:
            while stack and stack[-1].val == node.val:
                lastNode = stack.pop()
                inorderIndex += 1
                
            lastNode.right = node
            
        stack.append(node)
        
    return root

2. 输出二叉树的后序遍历的结点序列：

def postorderTraversal(root):
    if not root:
        return []
    
    result = []
    stack = [(root, False)]
    
    while stack:
        node, visited = stack.pop()
        if visited:
            result.append(node.val)
        else:
            stack.append((node, True))
            if node.right:
                stack.append((node.right, False))
            if node.left:
                stack.append((node.left, False))
                
    return result

3. 输出二叉树的叶子结点：

def getLeafNodes(root):
    if not root:
        return []
    
    result = []
    stack = [root]
    
    while stack:
        node = stack.pop()
        if not node.left and not node.right:
            result.append(node.val)
        else:
            if node.right:
                stack.append(node.right)
            if node.left:
                stack.append(node.left)
                
    return result

4. 统计二叉树的结点个数：

def getNodeCount(root):
    if not root:
        return 0
    
    count = 0
    stack = [root]
    
    while stack:
        node = stack.pop()
        count += 1
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)
            
    return count