非递归深度优先遍历树

以下是非递归深度优先遍历树的实现代码：

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

def preorderNonrecursion(root):
    if not root:
        return
    
    stack = []
    stack.append(root)
    
    while stack:
        node = stack.pop()
        visit(node)
        
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)

def visit(node):
    print(node.val)

# 创建一个示例树
#      1
#     / \
#    2   3
#   / \
#  4   5
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

preorderNonrecursion(root)

输出结果为：

1
2
4
5
3