def postorder_travel2(node):
"""后序遍历，非递归法"""
stack = Stack()
while node is not None or not stack.is_empty():
while node is not None: # 下行循环，直到栈顶元素为空
stack.push(node)
node = node.left if node.left is not None else node.right
node = stack.pop()
print(node, end=" ")
if not stack.is_empty() and stack.top(
).left == node: # 栈非空且当前节点是栈顶的左子节点
node = stack.top().right
else: # 没有右子树或右子树遍历完毕，强迫退栈
node = None
def preorder_travel2(node):
"""前序遍历，非递归法"""
stack = Stack()
while node is not None or not stack.is_empty():
while node is not None: # 沿左分支下行
print(node, end=" ")
stack.push(node.right) # 右分支入栈
node = node.left # 指针指向左分支
node = stack.pop() # 遇到空树，回溯
def inorder_travel2(node):
"""中序遍历，非递归法"""
stack = Stack()
while node is not None or not stack.is_empty():
while node is not None:
stack.push(node)
node = node.left if node.left is not None else node.right
node = stack.pop()
print(node, end=" ")
node = node.right
def dfs_graph(graph, v0):
"""深度优先图遍历"""
from queue_stack import Stack
vnum = graph.vertex_num()
visited = [0] * vnum # visited 记录已访问顶点
visited[v0] = 1
DFS_seq = [v0] # DFS_seq 记录遍历序列
st = Stack()
st.push((0, graph.out_edges(v0))) # 入栈 (i, edges)
while not st.is_empty(): # 下次访问边edges[i]
i, edges = st.pop()
if i < len(edges):
v, e = edges[i]
st.push((i + 1, edges)) # 下次回来访问边edges[i+1]
if not visited[v]:
DFS_seq.append(v)
visited[v] = 1
st.push((0, graph.out_edges(v)))
return DFS_seq