def delete(self, word):
# If tree is empty
if not self.root:
return False
# If trie is not empty
# Put the nodes in a stack
current = self.root
node_stack = Stack()
for char in word:
if char not in current.children:
return False
current = current.children[char]
node_stack.push(current)
if not current.is_end:
return False
# Delete node from the end of key if node does not have children
current.is_end = False
for i in range(node_stack.count()):
current = node_stack.pop()
prev = node_stack.peek()
if not current.children and prev:
del prev.children[current.char]
return True
def infix_to_postfix(infix):
"""
中缀转后缀
:param infix:中缀表达式
:return: 后缀表达式
"""
opstack = Stack() # 操作符栈
result = []
for token in infix:
if is_operand(token): # 操作数
result.append(token)
elif token == '(': # 遇到左括号，入栈
opstack.push(token)
elif token == ')': # 遇到右括号，弹栈并将值放至result列表末尾, 直到遇到左括号
_token = opstack.pop()
while _token and _token != '(':
result.append(_token)
_token = opstack.pop()
else: # 遇到操作符，压栈，但是如果在栈中有比当前操作符优先级高的任何操作符要先弹出
while not opstack.is_empty():
top_token = opstack.peek()
if higher_precedence(top_token, token):
result.append(opstack.pop())
else:
break
opstack.push(token)
while not opstack.is_empty():
result.append(opstack.pop())
return ''.join(result)
def test_peek_empty(self):
mystack = Stack()
result = mystack.peek()
self.assertEqual(result, None)
self.assertEqual(mystack.count(), 0)
def test_push(self):
mystack = Stack()
mystack.push('Python0')
self.assertEqual(mystack.count(), 1)
self.assertEqual(mystack.peek(), 'Python0')