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

def dfs1(root):
    if not root:
        return
    temp = []
    temp.append(root)
    while temp:
        node = temp[-1]
        temp.pop()
        print(node.val, end=" ")
        if node.right:
            temp.append(node.right)
        if node.left:
            temp.append(node.left)

def dfs2(root):
    if not root:
        return
    st = []
    st.append(root)
    while st:
        node = st[-1]
        st.pop()
        print(node.val, end=" ")
        if node.right:
            st.append(node.right)
        ——————————————————