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MayankShah1MayankShah1
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Done Chapter 6 Creativity questions
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‎.idea/workspace.xml

+224-137
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‎06-Stacks-Queues-Deques/Exercises/Creativity/C6-16.py

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class Empty(Exception):
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"""Error attempting to access an element from an empty container"""
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pass
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class Full(Exception):
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"""Error attempting to push an element to a full container."""
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pass
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class ArrayStack:
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"""LIFO Stack implementation using a Python list as underlying storage."""
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def __init__(self, maxlen = None):
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"""Create an empty stack."""
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self._data = []
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self._maxlen = maxlen
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def __len__(self):
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"""Return the number of elements in the stack."""
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return len(self._data)
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def is_empty(self):
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"""Return True if stack is empty."""
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return len(self._data) == 0
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def push(self, e):
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"""Add element e to the top of the stack."""
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if self._maxlen is not None and (self._maxlen == len(self._data)):
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raise Full('Stack is full')
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self._data.append(e)
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def top(self):
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"""Return the element at the top of the stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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return self._data[-1]
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def pop(self):
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"""Remove and return the element from the top of the Stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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return self._data.pop()
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def __str__(self):
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"""Prints the elements of stack"""
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result = ''.join(str(self._data[i]) + " " for i in range(len(self._data)))
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return result
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# Testing
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if __name__ == "__main__":
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S = ArrayStack(3)
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S.push(5)
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S.push(3)
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print(len(S))
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print(S)
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S.push(7)
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print(len(S))
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print(S)
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S.push(9)

‎06-Stacks-Queues-Deques/Exercises/Creativity/C6-17.py

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class Empty(Exception):
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"""Error attempting to access an element from an empty container"""
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pass
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class Full(Exception):
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"""Error attempting to push an element to a full container."""
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pass
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class ArrayStack:
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"""LIFO Stack implementation using a Python list as underlying storage."""
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def __init__(self, maxlen = None):
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"""Create an empty stack."""
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self._maxlen = maxlen
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if self._maxlen is not None:
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self._data = [None] * self._maxlen
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self._n = 0
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def __len__(self):
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"""Return the number of elements in the stack."""
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return self._n
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def is_empty(self):
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"""Return True if stack is empty."""
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return self._n == 0
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def push(self, e):
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"""Add element e to the top of the stack."""
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if self._maxlen is not None and (self._maxlen == self._n):
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raise Full('Stack is full')
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if self._data[self._n] is None:
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self._data[self._n] = e
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self._n += 1
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def top(self):
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"""Return the element at the top of the stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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return self._data[-1]
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def pop(self):
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"""Remove and return the element from the top of the Stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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answer = self._data[self._n-1]
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self._data[self._n-1] = None
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self._n -= 1
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return answer
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def __str__(self):
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"""Prints the elements of stack"""
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result = ''.join(str(self._data[i]) + " " for i in range(len(self._data)) if self._data[i] is not None)
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return result
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# Testing
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if __name__ == "__main__":
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S = ArrayStack(3)
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S.push(5)
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S.push(3)
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print(len(S))
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print(S)
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S.push(7)
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print(len(S))
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print(S)
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print(S.is_empty())
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print(S.pop())
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print(S.is_empty())
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print(S)
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S.push(9)
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print(S.top())
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print(S)
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print(len(S))
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print(S.pop())
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S.push(6)
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print(S)

‎06-Stacks-Queues-Deques/Exercises/Creativity/C6-18.py

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import stackarray as Stack
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def transfer(S, T):
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"""Transfer the contents of stack of S to stack T"""
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while not S.is_empty():
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T.push(S.pop())
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# Testing
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if __name__ == "__main__":
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S = Stack.ArrayStack()
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T = Stack.ArrayStack()
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U = Stack.ArrayStack()
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S.push(12)
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S.push(10)
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S.push(25)
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print('S initial : ',S)
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transfer(S,T)
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print(T)
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transfer(T,U)
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print(U)
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transfer(U,S)
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print('S after : ',S)

‎06-Stacks-Queues-Deques/Exercises/Creativity/C6-19.py

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import stackarray as Stack
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def is_matched_html(raw):
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"""Return True if all HTML tags are properly matched;False otherwise"""
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S = Stack.ArrayStack()
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j = raw.find('<')
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while j != -1:
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k = raw.find('>', j+1)
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if k == -1: # invalid tag
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return False
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tag = raw[j+1 : k] # strip away the tag
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space = tag.find(' ')
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if space != -1:
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tag = tag[0: space]
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if not tag.startswith('/'): # opening tag
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S.push(tag)
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else:
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if S.is_empty():
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return False
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if tag[1:] != S.pop():
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return False
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j = raw.find('<', k+1)
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return S.is_empty()
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# Testing
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if __name__ == "__main__":
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raw_html = open('/home/mayank/Desktop/Algorithms-in-Python/06-Stacks-Queues-Deques/Exercises/Creativity/sample.html')
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html_list = []
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for line in raw_html:
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html_list.append(line)
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html_str = ''.join(html_list)
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print(html_str)
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print(is_matched_html(html_str))

‎06-Stacks-Queues-Deques/Exercises/Creativity/C6-20.py

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import stackarray as Stack
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def postfix(expr):
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"""Returns the postfix expression of the given infix expr"""
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precedence = ['(',')','^','/','*','+','-']
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postfix_expr = []
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stack = Stack.ArrayStack()
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for char in expr:
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if char in precedence:
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if precedence.index(char) == 0: # opening paranthesis
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stack.push(char)
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elif precedence.index(char) == 1: # closing paranthesis
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while not stack.is_empty():
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res = stack.pop()
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if res == '(':
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break
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postfix_expr.append(res)
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else: # other operators
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if len(stack) > 0 and precedence.index(char) > precedence.index(stack.top()):
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while len(stack) > 0 and precedence.index(char) > precedence.index(stack.top()):
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if stack.top() != '(':
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postfix_expr.append(stack.pop())
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else:
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break
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stack.push(char)
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else:
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stack.push(char)
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else:
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postfix_expr.append(char)
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while not stack.is_empty():
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postfix_expr.append(stack.pop())
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return ''.join(postfix_expr)
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# Testing
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if __name__ == "__main__":
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print(postfix('(A+B)*(C-D)/(E*F)'))
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print(postfix('(A/B^C-D)'))

‎06-Stacks-Queues-Deques/Exercises/Creativity/__pycache__/stackarray.cpython-35.pyc

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‎06-Stacks-Queues-Deques/Exercises/Creativity/sample.html

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<html>
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<head>
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<title>Title</title>
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</head>
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<body>
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<center>
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<h1 attr = "hello"> The Little Boat </h1>
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</center>
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<p style="color:red;"> The storm tossed the little
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boat like a cheap sneaker in an
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old washing machine. The three
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drunken fishermen were used to
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such treatment, of course, but
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not the tree salesman, who even as
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a stowaway now felt that he
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had overpaid for the voyage. </p>
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<ol>
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<li> Will the salesman die? </li>
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<li> What color is the boat? </li>
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<li> And what about Naomi? </li>
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</ol>
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</body>
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</html>

‎06-Stacks-Queues-Deques/Exercises/Creativity/stackarray.py

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class Empty(Exception):
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"""Error attempting to access an element from an empty container"""
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pass
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5+
class ArrayStack:
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"""LIFO Stack implementation using a Python list as underlying storage."""
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8+
def __init__(self):
9+
"""Create an empty stack."""
10+
self._data = []
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12+
def __len__(self):
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"""Return the number of elements in the stack."""
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return len(self._data)
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def is_empty(self):
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"""Return True if stack is empty."""
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return len(self._data) == 0
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def push(self,e):
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"""Add element e to the top of the stack."""
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self._data.append(e)
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def top(self):
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"""Return the element at the top of the stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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return self._data[-1]
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def pop(self):
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"""Remove and return the element from the top of the Stack.
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Raise empty exception if the stack is empty.
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"""
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if self.is_empty():
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raise Empty('Stack is empty.')
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return self._data.pop()
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def __str__(self):
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"""Prints the elements of stack"""
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result = ''.join(str(self._data[i]) + " " for i in range(len(self._data)))
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return result
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# Testing
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if __name__ == "__main__":
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S = ArrayStack()
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S.push(5)
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S.push(3)
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print(len(S))
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print(S.pop())
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print(S.is_empty())
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print(S.pop())
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print(S.is_empty())
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S.push(7)
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S.push(9)
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print(S.top())
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S.push(4)
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print(len(S))
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print(S.pop())
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S.push(6)

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