def postorder_nonrec(t, proc):
s = SStack()
while t is not None or not s.is_empty():
while t is not None: # iterate until top has no child
s.push(t)
t = t.left if t.left is not None else t.right
# if we can go left, go, otherwise, go right
t = s.pop() # get the node to be access
proc(t.data)
if not s.is_empty() and s.top().left == t:
t = s.top().right # end of left visit, turn right
else:
t = None # end of right visit, force to backtrack
def preorder_iter(t):
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):
s = SStack()
while t is not None or not s.is_empty():
while t is not None: # go down along left chain
s.push(t.right) # push right branch into stack
proc(t.data)
t = t.left
t = s.pop() # left chain ends, backtrack
def inorder_nonrec(t, proc):
s = SStack()
while t is not None or not s.is_empty():
while t is not None:
s.push(t)
t = t.left
t = s.pop()
proc(t.data)
t = t.right
def trans_infix_suffix(line):
st = SStack()
llen = len(line)
exp = []
for x in tokens(line): # tokens 是一个待定义的生成器
if x not in infix_operators: # 运算对象直接送出
exp.append(x)
elif st.is_empty() or x == '(': # 左括号进栈
st.push(x)
elif x == ')': # 处理右括号的分支
while not st.is_empty() and st.top() != "(":
exp.append(st.pop())
if st.is_empty(): # 没找到左括号，就是不配对
raise SyntaxError("Missing \'(\'.")
st.pop() # 弹出左括号，右括号也不进栈
else: # 处理算术运算符，运算符都看作是左结合
while (not st.is_empty() and priority[st.top()] >= priority[x]):
exp.append(st.pop())
st.push(x) # 算术运算符进栈
while not st.is_empty(): # 送出栈里剩下的运算符
if st.top() == "(": # 如果还有左括号，就是不配对
raise SyntaxError("Extra \'(\' in expression.")
exp.append(st.pop())
return exp
def maze_solver1(maze, start, end):
st = SStack()
pos, nxt = start, 0
while True:
if pos == end:
print_path1(pos, st)
return
mark(maze, pos)
for i in range(nxt, 4): # 依次检查潜在探索方向
nextp = (pos[0] + dirs[i][0], pos[1] + dirs[i][1]) # 算出下一点
if passable(maze, nextp): # 遇到未探查点
st.push((pos, i + 1)) # 原位置进栈
pos, nxt = nextp, 0
break
else:
if st.is_empty():
break
pos, nxt = st.pop()
print("No path found.") # 找不到路径
def maze_solver(maze, start, end):
if start == end:
print(start)
return
st = SStack()
mark(maze, start)
st.push((start, 0)) # start position into stack 入口和方向 0 的序对入栈
while not st.is_empty(): # have possibility to try 走不通时回退
pos, nxt = st.pop() # get last branch position 取栈顶及其探查方向
for i in range(nxt, 4): # try to find unexploring dir(s) 依次检查未探查方向
nextp = (pos[0] + dirs[i][0], pos[1] + dirs[i][1]
) # next point 算出下一点
if nextp == end: # find end, great! :-) 到达出口,打印路径
print_path(end, pos, st)
return
if passable(maze, nextp): # new position is passable 遇到未探查的新位置
st.push((pos, i + 1)) # original position in stack 原位置和下一方向入栈
mark(maze, nextp)
st.push((nextp, 0)) # new position into stack 新位置入栈
break # 退出内层循环，下次迭代将以新栈顶为当前位置继续
print("No path.") # :-( 找不到路径