def postorder_nonrec(t, proc):
"""非递归后序遍历"""
s = SStack()
while t is not None or not s.is_empty():
while t is not None: # 下行循环，直到栈顶的两子树空
s.push(t)
t = t.left if t.left is not None else t.right
# 能左就左，否则向右一步
t = s.pop()
proc(t.data)
if not s.is_empty() and s.top().left == t:
t = s.top().right # 栈不空且当前结点是栈顶的左子结点
else:
t = None # 没有右子树或右子树遍历完毕，强迫退栈
def preorder_elements(t):
"""生成器遍历"""
s = SStack()
while t is not None or not s.is_empty():
while t is not None:
s.push(t.right)
yield t.data
t = t.left
t = s.pop()
def preorder_nonrec(t, proc):
"""先序循环法"""
s = SStack()
while t is not None or not s.is_empty():
while t is not None: # 沿左分支下行
proc(t.data) # 先根序先处理根数据
s.push(t.right) # 右分支如栈
t = t.left
t = s.pop() # 遇到空树，回溯
def DFS_graph(graph, v0):
""""深度优先的非递归算法"""
vnum = graph.vertex_num()
visited = [0] * vnum
visited[v0] = 1
DFS_seq = [v0]
st = SStack()
st.push((0, graph.out_edges(v0)))
while not st.is_empty():
i, edges = st.pop()
if i < len(edges):
v, e = edges[i] # pylint: disable=unused-variable
st.push((i + 1, edges))
if not visited[v]:
DFS_seq.append(v)
visited[v] = 1
st.push((0, graph.out_edges(v)))
return DFS_seq