如何进行二叉树的边界遍历。

pythonCopy codeclass TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def printLeftBoundary(root):
    if root is None:
        return

    if root.left is not None:
        print(root.val, end=' ')
        printLeftBoundary(root.left)
    elif root.right is not None:
        print(root.val, end=' ')
        printLeftBoundary(root.right)

def printRightBoundary(root):
    if root is None:
        return

    if root.right is not None:
        printRightBoundary(root.right)
        print(root.val, end=' ')
    elif root.left is not None:
        printRightBoundary(root.left)
        print(root.val, end=' ')

def printLeaves(root):
    if root is None:
        return

    printLeaves(root.left)

    if root.left is None and root.right is None:
        print(root.val, end=' ')

    printLeaves(root.right)

def printBoundary(root):
    if root is None:
        return

    print(root.val, end=' ')

    printLeftBoundary(root.left)
    printLeaves(root.left)
    printLeaves(root.right)
    printRightBoundary(root.right)