def test_pop(self):
s = Stack(['A', 'B', 'C'])
assert s.pop() == 'C'
assert s.length() == 2
assert s.pop() == 'B'
assert s.length() == 1
assert s.pop() == 'A'
assert s.length() == 0
assert s.is_empty() is True
with self.assertRaises(ValueError):
s.pop()
def test_length(self):
s = Stack()
assert s.length() == 0
s.push('A')
assert s.length() == 1
s.push('B')
assert s.length() == 2
s.pop()
assert s.length() == 1
s.pop()
assert s.length() == 0
def test_push(self):
s = Stack()
s.push('A')
assert s.peek() == 'A'
assert s.length() == 1
s.push('B')
assert s.peek() == 'B'
assert s.length() == 2
s.push('C')
assert s.peek() == 'C'
assert s.length() == 3
assert s.is_empty() is False
def reverse(nums):
#declare your stack
Stack = LinkedStack() #init the stack
#declare a variable to get track of the reversed number
reversed = []
#add each number in nums to the stack
for num in nums: # Loop through the whole list O(n)
if num == '-':
reversed.append(num) #adds sign to list O(1)
if num.isdigit():
Stack.push(num) #adds num to stack O(1)
#traverse through the stack
while Stack.length() > 0: # Loops through the whole stack
#add the head of the stack then delete the head
reversed.append(Stack.peek()) # adds number back to list O(1)
Stack.pop() # deletes current stack to move to the next one O(1)
if reversed[0] == '-':
if reversed[1] == '0':
reversed.pop(1) #removes a digit O(1)
if reversed[0] == '0':
reversed.pop(0) #removes a digit O(1)
return "".join(reversed)
def _traverse_in_order_iterative(self, node, visit):
"""Traverse this binary tree with iterative in-order traversal (DFS).
Start at the given node and visit each node with the given function.
Running time: O(n) since we visit every node
Memory usage: O(logn) for the depth of the tree"""
# -create an empty stack
# -curr variable which starts off with the self.root (will be updated in a while loop!!)
# -go in a while loop while true (will be false when the stack is empty)
# -call push() on curr while there's a value
# -update the curr to become the curr's left
# -once we hit a None value:
# - we'd want to pop() off the stack
# - append it to the list
# - update curr to be the recently popped node's right node
# - however, if the stack is empty in here, we set the while loop to false and exit the function!
stack = LinkedStack() # will act as the recursive call
curr = self.root # start at the root
stillLoop = True # loop until the stack is empty
while stillLoop:
# we're at the end of a leaf node
if curr == None:
if stack.length() > 0:
node = stack.pop()
visit(node.data)
curr = node.right
# our stack is empty so we can finally return once all the nodes have been visited
else:
stillLoop = False
# we can still go down the left side
else:
stack.push(curr)
curr = curr.left
def test_init(self):
s = Stack()
assert s.peek() is None
assert s.length() == 0
assert s.is_empty() is True
def test_init_with_list(self):
s = Stack(['A', 'B', 'C'])
assert s.peek() == 'C'
assert s.length() == 3
assert s.is_empty() is False
