def reverse_list(data):
"""Reverse the elements of list using stack"""
S = Stack.ArrayStack()
for i in range(len(data)):
S.push(data[i])
for i in range(len(data)):
data[i] = S.pop()
def reverse_file(filename):
"""Overwrite a a given file with its contents line-by-line reversed."""
S = Stack.ArrayStack()
original = open(filename)
for line in original:
S.push(line.rstrip('\n'))
original.close()
# Now we overwrite the file
output = open(filename, 'w')
while not S.is_empty():
output.write(S.pop() + '\n')
output.close()
def is_matched(expr):
"""Returns True if all the delimiters are matched properly;False otherwise."""
S = Stack.ArrayStack()
left = '({['
right = ')}]'
for c in expr:
if c in left:
S.push(c)
elif c in right:
if S.is_empty():
return False
if right.index(c) != left.index(S.pop()):
return False
return S.is_empty()
def is_matched_html(raw):
"""Return True if all HTML tags are properly matched;False otherwise"""
S = Stack.ArrayStack()
j = raw.find('<')
while j != -1:
k = raw.find('>', j + 1)
if k == -1: # invalid tag
return False
tag = raw[j + 1:k] # strip away the tag
if not tag.startswith('/'): # opening tag
S.push(tag)
else:
if S.is_empty():
return False
if tag[1:] != S.pop():
return False
j = raw.find('<', k + 1)
return S.is_empty()
def postfix(expr):
"""Returns the postfix expression of the given infix expr"""
precedence = ['(', ')', '^', '/', '*', '+', '-']
postfix_expr = []
stack = Stack.ArrayStack()
for char in expr:
if char in precedence:
if precedence.index(char) == 0: # opening paranthesis
stack.push(char)
elif precedence.index(char) == 1: # closing paranthesis
while not stack.is_empty():
res = stack.pop()
if res == '(':
break
postfix_expr.append(res)
else: # other operators
if len(stack) > 0 and precedence.index(
char) > precedence.index(stack.top()):
while len(stack) > 0 and precedence.index(
char) > precedence.index(stack.top()):
if stack.top() != '(':
postfix_expr.append(stack.pop())
else:
break
stack.push(char)
else:
stack.push(char)
else:
postfix_expr.append(char)
while not stack.is_empty():
postfix_expr.append(stack.pop())
return ''.join(postfix_expr)
def postfix_evaluate(expr):
"""Evaluate the given postfix operation"""
stack = Stack.ArrayStack()
operators = ['*', '+', '-', '/', '^']
for char in expr:
if char not in operators:
stack.push(int(char))
else:
num1 = stack.pop()
num2 = stack.pop()
if char == '+':
stack.push(num1 + num2)
elif char == '-':
stack.push(num2 - num1)
elif char == '*':
stack.push(num1 * num2)
elif char == '/':
stack.push(num2 // num1)
return stack.top()
import stackarray as Stack
def transfer(S, T):
"""Transfer the contents of stack of S to stack T"""
while not S.is_empty():
T.push(S.pop())
# Testing
if __name__ == "__main__":
S = Stack.ArrayStack()
T = Stack.ArrayStack()
U = Stack.ArrayStack()
S.push(12)
S.push(10)
S.push(25)
print('S initial : ', S)
transfer(S, T)
print(T)
transfer(T, U)
print(U)
transfer(U, S)
print('S after : ', S)
import stackarray as Stack
def empty_stack(S):
"""Empty the stack"""
if S.is_empty():
return
else:
print('Item popped: ', S.pop())
empty_stack(S)
# Testing
if __name__ == "__main__":
S = Stack.ArrayStack()
S.push(12)
S.push(10)
S.push(25)
print(S)
empty_stack(S)
print("Length of stack S: ", len(S))