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stack.py
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114 lines (96 loc) · 3.54 KB
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# Author: OMKAR PATHAK
# Created On: 3rd August 2017
# stack implementation
class Stack(object):
'''
size : return the current size of the stack
push : push an item into the stack
pop : pop the topmost item from the stack
peek : return the topmost element of the stack
isEmpty : check if the stack is empty
'''
def __init__(self, limit = 10):
'''
@param : limit: the stack size
'''
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:
return -1 # indicates stack overflow
else:
self.stack.append(data)
# for popping the uppermost element
def pop(self):
if len(self.stack) <= 0:
return -1 # indicates stack underflow
else:
return self.stack.pop()
# for peeking the top-most element of the stack
def peek(self):
if len(self.stack) <= 0:
return -1 # stack underflow
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)
# easily retrieve the source code of the Stack class
def get_code(self):
import inspect
return inspect.getsource(Stack)
class InfixToPostfix(object):
'''
infix_to_postfix : get the postfix of the given infix expression
'''
def __init__(self, expression = [], stack = None):
'''
@param: expression : the infix expression to be converted to postfix
@param: stack : stack to perform infix to postfix operation
'''
self.myExp = list(expression)
self.myStack = stack
# function to check whether the given character of the expression is operand
def _isOperand(self, char):
return (ord(char) >= ord('a') and ord(char) <= ord('z')) or (ord(char) >= ord('A') and ord(char) <= ord('Z'))
# self defined precedence for each operator
def _precedence(self, char):
if char == '+' or char == '-':
return 1
elif char == '*' or char == '/':
return 2
elif char == '^':
return 3
else:
return -1
# function to convert infix to postfix
def infix_to_postfix(self):
postFix = []
for i in range(len(self.myExp)):
if (self._isOperand(self.myExp[i])):
postFix.append(self.myExp[i])
elif(self.myExp[i] == '('):
self.myStack.push(self.myExp[i])
elif(self.myExp[i] == ')'):
topOperator = self.myStack.pop()
while(not self.myStack.isEmpty() and topOperator != '('):
postFix.append(topOperator)
topOperator = self.myStack.pop()
else:
while (not self.myStack.isEmpty()) and (self._precedence(self.myExp[i]) <= self._precedence(self.myStack.peek())):
postFix.append(self.myStack.pop())
self.myStack.push(self.myExp[i])
while(not self.myStack.isEmpty()):
postFix.append(self.myStack.pop())
return ' '.join(postFix)
# easily retrieve the source code of the Stack class
def get_code(self):
import inspect
return inspect.getsource(InfixToPostfix)