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MY_BOOK/ebook_src/abstract_structures/stacks/dec2bin_with_stack.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+'''transform a decimal number to a binary number with a stack '''
+
+
+from stack import Stack
+
+def dec2bin_with_stack(decnum):
+
+    s = Stack()
+    str_aux = ''
+
+    while decnum > 0:
+        dig = decnum % 2
+        decnum = decnum//2
+        s.push(dig)
+
+    while not s.isEmpty():
+        str_aux += str(s.pop())
+
+    return str_aux
+
+
+
+if __name__ == '__main__':
+    decnum = 9
+    assert(dec2bin_with_stack(decnum) == '1001')

MY_BOOK/ebook_src/abstract_structures/stacks/linked_stack.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+""" A stack made of linked list"""
+
+
+class Node(object):
+    def __init__(self, value=None, pointer=None):
+        self.value = value
+        self.pointer = pointer
+
+
+class Stack(object):
+    def __init__(self):
+        self.head = None
+
+    def isEmpty(self):
+        return not bool(self.head)
+
+    def push(self, item):
+        self.head = Node(item, self.head)
+
+
+    def pop(self):
+        if self.head:
+            node = self.head
+            self.head = node.pointer
+            return node.value
+        else:
+            print('Stack is empty.')
+
+
+    def peek(self):
+        if self.head:
+            return self.head.value
+        else:
+            print('Stack is empty.')
+
+
+    def size(self):
+        node = self.head
+        count = 0
+        while node:
+            count +=1
+            node = node.pointer
+        return count
+
+
+    def _printList(self):
+        node = self.head
+        while node:
+            print(node.value)
+            node = node.pointer
+
+
+
+if __name__ == '__main__':
+    stack = Stack()
+    print("Is the stack empty? ", stack.isEmpty())
+    print("Adding 0 to 10 in the stack...")
+    for i in range(10):
+        stack.push(i)
+    stack._printList()
+    print("Stack size: ", stack.size())
+    print("Stack peek : ", stack.peek())
+    print("Pop...", stack.pop())
+    print("Stack peek: ", stack.peek())
+    print("Is the stack empty? ", stack.isEmpty())
+    stack._printList()

MY_BOOK/ebook_src/abstract_structures/stacks/reverse_string_with_stack.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+''' Uses a stack to reverse a string '''
+
+from stack import Stack
+
+def reverse_string_with_stack(str1):
+
+  s = Stack()
+  revStr = ''
+
+  for c in str1:
+    s.push(c)
+
+  while not s.isEmpty():
+    revStr += s.pop()
+
+  return revStr
+
+
+
+if __name__ == '__main__':
+  str1 = 'Buffy is a Slayer!'
+  print(str1)
+  print(reverse_string_with_stack(str1))
+
+
+

MY_BOOK/ebook_src/abstract_structures/stacks/set_of_stacks.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+""" define a class for a set of stacks """
+
+from stack import Stack
+
+class SetOfStacks(Stack):
+    def __init__(self, capacity=4):
+        self.setofstacks = []
+        self.items = []
+        self.capacity = capacity
+
+
+    def push(self, value):
+        if self.size() >= self.capacity:
+            self.setofstacks.append(self.items)
+            self.items = []
+        self.items.append(value)
+
+
+    def pop(self):
+        value = self.items.pop()
+        if self.isEmpty() and self.setofstacks:
+            self.items = self.setofstacks.pop()
+        return value
+
+
+    def sizeStack(self):
+        return len(self.setofstacks)*self.capacity + self.size()
+
+
+    def __repr__(self):
+        aux = []
+        for s in self.setofstacks:
+             aux.extend(s)
+        aux.extend(self.items)
+        return '{}'.format(aux)
+
+
+
+if __name__ == '__main__':
+    capacity = 5
+    stack = SetOfStacks(capacity)
+    print("Is the stack empty? ", stack.isEmpty())
+    print("Adding 0 to 10 in the stack...")
+    for i in range(10):
+        stack.push(i)
+    print(stack)
+    print("Stack size: ", stack.sizeStack())
+    print("Stack peek : ", stack.peek())
+    print("Pop...", stack.pop())
+    print("Stack peek: ", stack.peek())
+    print("Is the stack empty? ", stack.isEmpty())
+    print(stack)

MY_BOOK/ebook_src/abstract_structures/stacks/stack.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+# copy of the class ../Stack.py
+
+__author__ = "bt3"
+
+
+class Stack(object):
+    def __init__(self):
+        self.content = []
+        self.min_array = []
+        self.min = float('inf')
+
+    def push(self, value):
+        if value < self.min:
+            self.min = value
+
+        self.content.append(value)
+        self.min_array.append(self.min)
+
+    def pop(self):
+        if self.content:
+            value = self.content.pop()
+            self.min_array.pop()
+            if self.min_array:
+                self.min = self.min_array[-1]
+            return value
+        else:
+            return 'Empty List. '
+
+    def find_min(self):
+        if self.min_array:
+            return self.min_array[-1]
+        else:
+            return 'No min value for empty list.'
+
+    def size(self):
+        return len(self.content)
+
+    def isEmpty(self):
+        return not bool(self.content)
+
+    def peek(self):
+        if self.content:
+            return self.content[-1]
+        else:
+            print('Stack is empty.')
+
+
+    def __repr__(self):
+        return '{}'.format(self.content)
+
+
+if __name__ == '__main__':
+    q = Stack()
+
+    for i in range(15,20):
+        q.push(i)
+    for i in range(10,5,-1):
+        q.push(i)
+
+
+
+    for i in range(1, 13):
+        print q.pop(), q.find_min()

MY_BOOK/ebook_src/abstract_structures/stacks/stack_with_min.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+''' A stack with a minimum lookup '''
+
+from stack import Stack
+
+
+class NodeWithMin(object):
+    def __init__(self, value=None, minimum=None):
+        self.value = value
+        self.minimum = minimum
+
+
+class StackMin(Stack):
+    def __init__(self):
+        self.items = []
+        self.minimum = None
+
+
+    def push(self, value):
+        if self.isEmpty() or self.minimum > value:
+           self.minimum = value
+        self.items.append(NodeWithMin(value, self.minimum))
+
+
+    def peek(self):
+        return self.items[-1].value
+
+
+    def peekMinimum(self):
+        return self.items[-1].minimum
+
+
+    def pop(self):
+        item = self.items.pop()
+        if item:
+            if item.value == self.minimum:
+                self.minimum = self.peekMinimum()
+            return item.value
+        else:
+            print("Stack is empty.")
+
+    def __repr__(self):
+        aux = []
+        for i in self.items:
+            aux.append(i.value)
+        return '{}'.format(aux)
+
+
+
+if __name__ == '__main__':
+    stack = StackMin()
+    print("Is the stack empty? ", stack.isEmpty())
+    print("Adding 0 to 10 in the stack...")
+    for i in range(10,3, -1):
+        stack.push(i)
+    print(stack)
+
+    print("Stack size: ", stack.size())
+    print("Stack peek and peekMinimum : ", stack.peek(), stack.peekMinimum())
+    print("Pop...", stack.pop())
+    print("Stack peek and peekMinimum : ", stack.peek(), stack.peekMinimum())
+    print("Is the stack empty? ", stack.isEmpty())
+    print(stack)
+
+    for i in range(5, 1, -1):
+        stack.push(i)
+    print(stack)
+
+    print("Stack size: ", stack.size())
+    print("Stack peek and peekMinimum : ", stack.peek(), stack.peekMinimum())
+    print("Pop...", stack.pop())
+    print("Stack peek and peekMinimum : ", stack.peek(), stack.peekMinimum())
+    print("Is the stack empty? ", stack.isEmpty())
+    print(stack)

MY_BOOK/ebook_src/abstract_structures/stacks/towers_of_hanoi.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+
+""" Implement the 'towers of hanoi'"""
+
+from linked_stack import Stack, Node
+
+
+def moveTop(s1, s3):
+
+    s3.append(s1.pop())
+
+
+def moveDisks(n, s1, s3, s2):
+
+    if n < 1: return
+    moveDisks(n - 1, s1, s2, s3)
+    moveTop(s1, s3)
+    moveDisks(n -1, s2, s3, s1)
+
+
+
+def towersOfHanoi(n):
+    s1 = [x+1 for x in range(n)]
+    s2 = []
+    s3 = []
+    print('The first stick is {0} and the third stick has {1}'.format(s1, s3))
+
+    moveDisks(n, s1, s3, s2)
+
+    print('The first stick is {0} and the third stick has {1}'.format(s1, s3))
+
+    return s3
+
+
+
+if __name__ == '__main__':
+    towersOfHanoi(6)