def suf_exp_evaluator(exp):
operators = '+-*/'
st = SStack()
for x in exp:
if x not in operators:
st.push(x)
continue
if st.depth() < 2:
raise ValueError
a = int(st.pop())
b = int(st.pop())
if x == '+':
c = b + a
elif x == '-':
c = b - a
elif x == '*':
c = b * a
elif x == '/':
c = b / a
else:
break
st.push(c)
if st.depth() == 1:
return st.pop()
raise ValueError
def check_parens(text):
parents = '(){}[]'
open_parents = '({['
oppsite = {')': '(', "]": '[', '}': '{'}
def parentsheses(text):
i, text_len = 0, len(text)
while True:
while i < len(text) and text[i] not in parents:
i += 1
if i >= text_len:
return
yield text[i], i
i += 1
ss = SStack()
for pr, i in parentsheses(text):
if pr in open_parents:
ss.push(pr)
elif ss.pop() != oppsite[pr]:
print('匹配错误%s' % pr)
return False
print('匹配正确，括号正确')
return True
def preorder(self):
t, s = self._root, SStack()
while t is not None or not s.is_empty():
while t is not None:
s.push(t.right)
yield t.data #此处应该有错误，没有定义过t的data属性 self._root=rootnode 作者
# 应该是认为rootnode是使用前面结点类创建的节点，那么这样就有data属性了
t = t.left
t = s.pop()
def entries(self):
t, s = self._root, 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()
yield t.data.key, t.data.value,
t = t.rignt
def maze_solve(maze, start, end):
if start == end:
print(start)
return
st = SStack()
mark(maze, start)
st.push((start, 0))
while not st.is_empty():
pos, nxt = st.pop()
for i in range(0, 4):
nexp = pos[0] + dirs[i][0], pos[1] + dirs[i][1]
if nexp == end:
print_path(end, pos, st)
elif passable(maze, nexp):
st.push((pos, i + 1))
mark(maze, pos)
st.push((nexp, 0))
break
print('no path')
def postorder_nonrec(t, proc):
s = SStack()
while t is not None or not s.is_empty():
while t is not None: # 下行，直到找到栈顶的两子数为空
s.push(t)
t = t.left if t.left is not None else t.ringt # 这里不用 try，如果t下面没有子树不会报错，而是None
# 看结点定义def __init__(self,dat,right=None,left=None)
t = s.pop()
proc(t.data)
if not s.is_empty() and s.top.left == t: # 如果t是现在栈顶的左子树
t = s.top().right
else:
t = None #
def preorder_elements(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: # 直到左枝为空
proc(t.data)
s.push(t.right)
t = t.left
t = s.pop()
def norec_fact(n):
res = 1
st = SStack()
while n > 0:
st.push(n)
n -= 1
while not st.is_empty():
res *= st.pop()
return res
def trans_infix_suffix(line):
st = SStack()
exp = []
for x in token(line):
if x not in infix_operators:
exp.append(x)
elif st.is_empty() or x == '(':
st.push(x)
elif x == ')':
while not st.is_empty() and st.top() != '(':
st.append(st.pop())
if st.is_empty():
raise ValueError
st.pop()
else:
while (not st.is_empty() and property[st.top()] >= property[x]
): # 当top是*/，x是+-的时候，将top加入
exp.append(st.pop())
st.push(x)
while not st.is_empty():
if st.top() == '(':
raise ValueError
exp.append(st.pop())
return exp