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Merge pull request #146 from chrismclennon/stack

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Refactor data_structures.Stacks
This commit is contained in:
Harshil 2017-10-19 09:37:57 +05:30 committed by GitHub
commit 606e69682f
6 changed files with 151 additions and 125 deletions
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27
data_structures/Stacks/Balanced_Parentheses.py
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# Author: OMKAR PATHAK
import Stack
def parseParenthesis(string):
balanced = 1
index = 0
myStack = Stack.Stack(len(string))
while (index < len(string)) and (balanced == 1):
check = string[index]
if check == '(':
myStack.push(check)
else:
if myStack.isEmpty():
balanced = 0
else:
myStack.pop()
index += 1
if balanced == 1 and myStack.isEmpty():
return True
else:
return False
if __name__ == '__main__':
print(parseParenthesis('((()))')) # True
print(parseParenthesis('((())')) # False

48
data_structures/Stacks/Infix_To_Postfix_Conversion.py
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# Author: OMKAR PATHAK
import Stack
def isOperand(char):
return (ord(char) >= ord('a') and ord(char) <= ord('z')) or (ord(char) >= ord('A') and ord(char) <= ord('Z'))
def precedence(char):
if char == '+' or char == '-':
return 1
elif char == '*' or char == '/':
return 2
elif char == '^':
return 3
else:
return -1
def infixToPostfix(myExp, myStack):
postFix = []
for i in range(len(myExp)):
if (isOperand(myExp[i])):
postFix.append(myExp[i])
elif(myExp[i] == '('):
myStack.push(myExp[i])
elif(myExp[i] == ')'):
topOperator = myStack.pop()
while(not myStack.isEmpty() and topOperator != '('):
postFix.append(topOperator)
topOperator = myStack.pop()
else:
while (not myStack.isEmpty()) and (precedence(myExp[i]) <= precedence(myStack.peek())):
postFix.append(myStack.pop())
myStack.push(myExp[i])
while(not myStack.isEmpty()):
postFix.append(myStack.pop())
return ' '.join(postFix)
if __name__ == '__main__':
myExp = 'a+b*(c^d-e)^(f+g*h)-i'
myExp = [i for i in myExp]
print('Infix:',' '.join(myExp))
myStack = Stack.Stack(len(myExp))
print('Postfix:',infixToPostfix(myExp, myStack))
# OUTPUT:
# Infix: a + b * ( c ^ d - e ) ^ ( f + g * h ) - i
# Postfix: a b c d ^ e - f g h * + ^ * + i -

50
data_structures/Stacks/Stack.py
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# Author: OMKAR PATHAK
class Stack(object):
def __init__(self, limit = 10):
self.stack = []
self.limit = limit
# for printing the stack contents
def __str__(self):
return ' '.join([str(i) for i in self.stack])
# for pushing an element on to the stack
def push(self, data):
if len(self.stack) >= self.limit:
print('Stack Overflow')
else:
self.stack.append(data)
# for popping the uppermost element
def pop(self):
if len(self.stack) <= 0:
return -1
else:
return self.stack.pop()
# for peeking the top-most element of the stack
def peek(self):
if len(self.stack) <= 0:
return -1
else:
return self.stack[len(self.stack) - 1]
# to check if stack is empty
def isEmpty(self):
return self.stack == []
# for checking the size of stack
def size(self):
return len(self.stack)
if __name__ == '__main__':
myStack = Stack()
for i in range(10):
myStack.push(i)
print(myStack)
myStack.pop() # popping the top element
print(myStack)
myStack.peek() # printing the top element
myStack.isEmpty()
myStack.size()

21
data_structures/Stacks/balanced_parentheses.py Normal file
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from Stack import Stack
__author__ = 'Omkar Pathak'
def balanced_parentheses(parentheses):
""" Use a stack to check if a string of parentheses are balanced."""
stack = Stack(len(parentheses))
for parenthesis in parentheses:
if parenthesis == '(':
stack.push(parenthesis)
elif parenthesis == ')':
stack.pop()
return not stack.is_empty()
if __name__ == '__main__':
examples = ['((()))', '((())']
print('Balanced parentheses demonstration:\n')
for example in examples:
print(example + ': ' + str(balanced_parentheses(example)))

62
data_structures/Stacks/infix_to_postfix_conversion.py Normal file
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import string
from Stack import Stack
__author__ = 'Omkar Pathak'
def is_operand(char):
return char in string.ascii_letters or char in string.digits
def precedence(char):
""" Return integer value representing an operator's precedence, or
order of operation.
https://en.wikipedia.org/wiki/Order_of_operations
"""
dictionary = {'+': 1, '-': 1,
'*': 2, '/': 2,
'^': 3}
return dictionary.get(char, -1)
def infix_to_postfix(expression):
""" Convert infix notation to postfix notation using the Shunting-yard
algorithm.
https://en.wikipedia.org/wiki/Shunting-yard_algorithm
https://en.wikipedia.org/wiki/Infix_notation
https://en.wikipedia.org/wiki/Reverse_Polish_notation
"""
stack = Stack(len(expression))
postfix = []
for char in expression:
if is_operand(char):
postfix.append(char)
elif char not in {'(', ')'}:
while (not stack.is_empty()
and precedence(char) <= precedence(stack.peek())):
postfix.append(stack.pop())
stack.push(char)
elif char == '(':
stack.push(char)
elif char == ')':
while not stack.is_empty() and stack.peek() != '(':
postfix.append(stack.pop())
# Pop '(' from stack. If there is no '(', there is a mismatched
# parentheses.
if stack.peek() != '(':
raise ValueError('Mismatched parentheses')
stack.pop()
while not stack.is_empty():
postfix.append(stack.pop())
return ' '.join(postfix)
if __name__ == '__main__':
expression = 'a+b*(c^d-e)^(f+g*h)-i'
print('Infix to Postfix Notation demonstration:\n')
print('Infix notation: ' + expression)
print('Postfix notation: ' + infix_to_postfix(expression))

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data_structures/Stacks/stack.py Normal file
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__author__ = 'Omkar Pathak'
class Stack(object):
""" A stack is an abstract data type that serves as a collection of
elements with two principal operations: push() and pop(). push() adds an
element to the top of the stack, and pop() removes an element from the top
of a stack. The order in which elements come off of a stack are
Last In, First Out (LIFO).
https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
"""
def __init__(self, limit=10):
self.stack = []
self.limit = limit
def __bool__(self):
return not bool(self.stack)
def __str__(self):
return str(self.stack)
def push(self, data):
""" Push an element to the top of the stack."""
if len(self.stack) >= self.limit:
raise StackOverflowError
self.stack.append(data)
def pop(self):
""" Pop an element off of the top of the stack."""
if self.stack:
return self.stack.pop()
else:
raise IndexError('pop from an empty stack')
def peek(self):
""" Peek at the top-most element of the stack."""
if self.stack:
return self.stack[-1]
def is_empty(self):
""" Check if a stack is empty."""
return not bool(self.stack)
def size(self):
""" Return the size of the stack."""
return len(self.stack)
class StackOverflowError(BaseException):
pass
if __name__ == '__main__':
stack = Stack()
for i in range(10):
stack.push(i)
print('Stack demonstration:\n')
print('Initial stack: ' + str(stack))
print('pop(): ' + str(stack.pop()))
print('After pop(), the stack is now: ' + str(stack))
print('peek(): ' + str(stack.peek()))
stack.push(100)
print('After push(100), the stack is now: ' + str(stack))
print('is_empty(): ' + str(stack.is_empty()))
print('size(): ' + str(stack.size()))