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Merge pull request #146 from chrismclennon/stack
Refactor data_structures.Stacks
This commit is contained in:
Harshil
GitHub
commit
606e69682f
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# Author: OMKAR PATHAK
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import Stack
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def parseParenthesis(string):
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balanced = 1
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index = 0
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myStack = Stack.Stack(len(string))
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while (index < len(string)) and (balanced == 1):
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check = string[index]
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if check == '(':
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myStack.push(check)
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else:
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if myStack.isEmpty():
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balanced = 0
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else:
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myStack.pop()
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index += 1
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if balanced == 1 and myStack.isEmpty():
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return True
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else:
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return False
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if __name__ == '__main__':
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print(parseParenthesis('((()))')) # True
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print(parseParenthesis('((())')) # False
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# Author: OMKAR PATHAK
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import Stack
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def isOperand(char):
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return (ord(char) >= ord('a') and ord(char) <= ord('z')) or (ord(char) >= ord('A') and ord(char) <= ord('Z'))
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def precedence(char):
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if char == '+' or char == '-':
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return 1
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elif char == '*' or char == '/':
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return 2
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elif char == '^':
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return 3
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else:
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return -1
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def infixToPostfix(myExp, myStack):
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postFix = []
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for i in range(len(myExp)):
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if (isOperand(myExp[i])):
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postFix.append(myExp[i])
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elif(myExp[i] == '('):
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myStack.push(myExp[i])
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elif(myExp[i] == ')'):
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topOperator = myStack.pop()
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while(not myStack.isEmpty() and topOperator != '('):
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postFix.append(topOperator)
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topOperator = myStack.pop()
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else:
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while (not myStack.isEmpty()) and (precedence(myExp[i]) <= precedence(myStack.peek())):
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postFix.append(myStack.pop())
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myStack.push(myExp[i])
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while(not myStack.isEmpty()):
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postFix.append(myStack.pop())
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return ' '.join(postFix)
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if __name__ == '__main__':
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myExp = 'a+b*(c^d-e)^(f+g*h)-i'
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myExp = [i for i in myExp]
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print('Infix:',' '.join(myExp))
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myStack = Stack.Stack(len(myExp))
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print('Postfix:',infixToPostfix(myExp, myStack))
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# OUTPUT:
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# Infix: a + b * ( c ^ d - e ) ^ ( f + g * h ) - i
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# Postfix: a b c d ^ e - f g h * + ^ * + i -
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@ -1,50 +0,0 @@
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# Author: OMKAR PATHAK
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class Stack(object):
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def __init__(self, limit = 10):
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self.stack = []
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self.limit = limit
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# for printing the stack contents
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def __str__(self):
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return ' '.join([str(i) for i in self.stack])
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# for pushing an element on to the stack
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def push(self, data):
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if len(self.stack) >= self.limit:
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print('Stack Overflow')
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else:
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self.stack.append(data)
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# for popping the uppermost element
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def pop(self):
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if len(self.stack) <= 0:
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return -1
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else:
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return self.stack.pop()
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# for peeking the top-most element of the stack
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def peek(self):
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if len(self.stack) <= 0:
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return -1
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else:
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return self.stack[len(self.stack) - 1]
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# to check if stack is empty
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def isEmpty(self):
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return self.stack == []
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# for checking the size of stack
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def size(self):
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return len(self.stack)
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if __name__ == '__main__':
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myStack = Stack()
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for i in range(10):
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myStack.push(i)
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print(myStack)
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myStack.pop() # popping the top element
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print(myStack)
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myStack.peek() # printing the top element
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myStack.isEmpty()
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myStack.size()
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21
data_structures/Stacks/balanced_parentheses.py
Normal file
21
data_structures/Stacks/balanced_parentheses.py
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from Stack import Stack
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__author__ = 'Omkar Pathak'
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def balanced_parentheses(parentheses):
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""" Use a stack to check if a string of parentheses are balanced."""
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stack = Stack(len(parentheses))
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for parenthesis in parentheses:
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if parenthesis == '(':
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stack.push(parenthesis)
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elif parenthesis == ')':
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stack.pop()
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return not stack.is_empty()
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if __name__ == '__main__':
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examples = ['((()))', '((())']
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print('Balanced parentheses demonstration:\n')
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for example in examples:
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print(example + ': ' + str(balanced_parentheses(example)))
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62
data_structures/Stacks/infix_to_postfix_conversion.py
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62
data_structures/Stacks/infix_to_postfix_conversion.py
Normal file
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import string
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from Stack import Stack
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__author__ = 'Omkar Pathak'
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def is_operand(char):
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return char in string.ascii_letters or char in string.digits
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def precedence(char):
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""" Return integer value representing an operator's precedence, or
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order of operation.
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https://en.wikipedia.org/wiki/Order_of_operations
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"""
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dictionary = {'+': 1, '-': 1,
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'*': 2, '/': 2,
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'^': 3}
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return dictionary.get(char, -1)
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def infix_to_postfix(expression):
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""" Convert infix notation to postfix notation using the Shunting-yard
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algorithm.
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https://en.wikipedia.org/wiki/Shunting-yard_algorithm
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https://en.wikipedia.org/wiki/Infix_notation
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https://en.wikipedia.org/wiki/Reverse_Polish_notation
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"""
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stack = Stack(len(expression))
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postfix = []
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for char in expression:
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if is_operand(char):
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postfix.append(char)
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elif char not in {'(', ')'}:
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while (not stack.is_empty()
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and precedence(char) <= precedence(stack.peek())):
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postfix.append(stack.pop())
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stack.push(char)
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elif char == '(':
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stack.push(char)
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elif char == ')':
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while not stack.is_empty() and stack.peek() != '(':
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postfix.append(stack.pop())
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# Pop '(' from stack. If there is no '(', there is a mismatched
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# parentheses.
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if stack.peek() != '(':
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raise ValueError('Mismatched parentheses')
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stack.pop()
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while not stack.is_empty():
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postfix.append(stack.pop())
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return ' '.join(postfix)
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if __name__ == '__main__':
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expression = 'a+b*(c^d-e)^(f+g*h)-i'
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print('Infix to Postfix Notation demonstration:\n')
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print('Infix notation: ' + expression)
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print('Postfix notation: ' + infix_to_postfix(expression))
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68
data_structures/Stacks/stack.py
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68
data_structures/Stacks/stack.py
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__author__ = 'Omkar Pathak'
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class Stack(object):
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""" A stack is an abstract data type that serves as a collection of
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elements with two principal operations: push() and pop(). push() adds an
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element to the top of the stack, and pop() removes an element from the top
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of a stack. The order in which elements come off of a stack are
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Last In, First Out (LIFO).
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https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
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"""
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def __init__(self, limit=10):
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self.stack = []
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self.limit = limit
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def __bool__(self):
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return not bool(self.stack)
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def __str__(self):
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return str(self.stack)
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def push(self, data):
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""" Push an element to the top of the stack."""
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if len(self.stack) >= self.limit:
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raise StackOverflowError
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self.stack.append(data)
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def pop(self):
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""" Pop an element off of the top of the stack."""
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if self.stack:
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return self.stack.pop()
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else:
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raise IndexError('pop from an empty stack')
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def peek(self):
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""" Peek at the top-most element of the stack."""
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if self.stack:
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return self.stack[-1]
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def is_empty(self):
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""" Check if a stack is empty."""
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return not bool(self.stack)
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def size(self):
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""" Return the size of the stack."""
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return len(self.stack)
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class StackOverflowError(BaseException):
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pass
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if __name__ == '__main__':
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stack = Stack()
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for i in range(10):
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stack.push(i)
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print('Stack demonstration:\n')
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print('Initial stack: ' + str(stack))
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print('pop(): ' + str(stack.pop()))
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print('After pop(), the stack is now: ' + str(stack))
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print('peek(): ' + str(stack.peek()))
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stack.push(100)
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print('After push(100), the stack is now: ' + str(stack))
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print('is_empty(): ' + str(stack.is_empty()))
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print('size(): ' + str(stack.size()))
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