def validate_string(string):
stack = Stack()
# opening symbols
opening = '{[('
# closing symbols, must be in the matched order of opening
closing = '}])'
# iterate through the string we are testing
for char in string:
# if we encounter an opening symbol, push it to the stack
if char in opening:
stack.push(char)
# if we encounter a closing symbol, check if it matches the top of the stack
elif char in closing:
i = closing.index(char)
if stack.is_empty() or stack.pop() != opening[i]:
return False
# if we've not matched all the symbols... fail!
if not stack.is_empty:
return False
# we have matched all the symbols, success!
return True
def test_check_not_empty():
s = Stack()
s.push("apple")
s.push("banana")
actual = s.is_empty()
expected = False
assert actual == expected
def test_pop_until_empty():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
s.pop()
s.pop()
s.pop()
actual = s.is_empty()
expected = True
assert actual == expected
def test_pop_till_empty():
stack = Stack()
stack.push('Dwight')
stack.push('Michael')
stack.push('Jim')
stack.pop()
stack.pop()
stack.pop()
actual = stack.is_empty()
expected = True
assert actual == expected
class PsuedoQueue:
"""
This is a queue being implement using stack's
push, pop and peek methods rather than having
its own attributes and methods
"""
def __init__(self):
self.front_stack = Stack()
self.rear_stack = Stack()
# this is strictly here so that we may pass a test,
self.front = None
def peek(self):
return self.front_stack.peek()
def is_empty(self):
return self.front_stack.is_empty()
def enqueue(self, value=None):
node = Node(value)
if self.rear_stack.top:
self.rear_stack.top.next = node
self.rear_stack.top = node
if not self.front_stack.top:
self.front_stack.top = node
# next line is solely here to pass a test
self.front = self.front_stack.top
def dequeue(self):
# if the queue only holds one node, we must manually set the rear to None
if (self.rear_stack.top == self.front_stack.top):
self.rear_stack.top = None
value = self.front_stack.pop()
# next line is solely here to pass a test
self.front = self.front_stack.top
return value
def test_empty_stack():
stack = Stack()
assert stack.is_empty()
