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stack.py
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106 lines (90 loc) · 3.53 KB
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# Author: OMKAR PATHAK
# Created On: 3rd August 2017
# stack implementation
class Stack(object):
def __init__(self, limit = 10):
'''
@param : limit: the stack size
'''
self.stack = []
self.limit = limit
def __str__(self):
return ' '.join([str(i) for i in self.stack])
def push(self, data):
''' pushes an item into the stack '''
if len(self.stack) >= self.limit:
return -1 # indicates stack overflow
else:
self.stack.append(data)
def pop(self):
''' pops the topmost item from the stack '''
if len(self.stack) <= 0:
return -1 # indicates stack underflow
else:
return self.stack.pop()
def peek(self):
''' returns the topmost element of the stack '''
if len(self.stack) <= 0:
return -1 # stack underflow
else:
return self.stack[len(self.stack) - 1]
def is_empty(self):
''' checks if the stack is empty '''
return self.size() == 0
def size(self):
''' returns the current size of the stack '''
return len(self.stack)
# easily retrieve the source code of the Stack class
def get_code(self):
''' returns the code for current class '''
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.expression = list(expression)
self.my_stack = stack
def _isOperand(self, char):
''' utility function to find whether the given character is an operator '''
return (ord(char) >= ord('a') and ord(char) <= ord('z')) or (ord(char) >= ord('A') and ord(char) <= ord('Z'))
def _precedence(self, char):
''' utility function to find precedence of the specified character '''
if char == '+' or char == '-':
return 1
elif char == '*' or char == '/':
return 2
elif char == '^':
return 3
else:
return -1
def infix_to_postfix(self):
''' function to generate postfix expression from infix expression '''
postfix = []
for i in range(len(self.expression)):
if (self._isOperand(self.expression[i])):
postfix.append(self.expression[i])
elif(self.expression[i] == '('):
self.my_stack.push(self.expression[i])
elif(self.expression[i] == ')'):
topOperator = self.my_stack.pop()
while(not self.my_stack.is_empty() and topOperator != '('):
postfix.append(topOperator)
topOperator = self.my_stack.pop()
else:
while (not self.my_stack.is_empty()) and (self._precedence(self.expression[i]) <= self._precedence(self.my_stack.peek())):
postfix.append(self.my_stack.pop())
self.my_stack.push(self.expression[i])
while(not self.my_stack.is_empty()):
postfix.append(self.my_stack.pop())
return ' '.join(postfix)
# easily retrieve the source code of the Stack class
def get_code(self):
''' returns the code of the current class '''
import inspect
return inspect.getsource(InfixTopostfix)