initial upload of all course files
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Joe James
BIN
Section_2/MaxHeap.pdf
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Section_2/MaxHeap.pdf
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Section_2/Stacks and Queues.pdf
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Section_2/Stacks and Queues.pdf
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Section_2/Stacks, Queues & Heaps.ipynb
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Section_2/Stacks, Queues & Heaps.ipynb
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Stacks, Queues & Heaps\n",
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"© Joe James, 2019.\n",
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"\n",
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"### Stack using Python List\n",
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"Stack is a LIFO data structure -- last-in, first-out. \n",
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"Use append() to push an item onto the stack. \n",
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"Use pop() to remove an item."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {
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"scrolled": true
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"[4, 7, 12, 19]\n"
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]
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}
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],
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"source": [
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"my_stack = list()\n",
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"my_stack.append(4)\n",
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"my_stack.append(7)\n",
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"my_stack.append(12)\n",
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"my_stack.append(19)\n",
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"print(my_stack)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"19\n",
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"12\n",
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"[4, 7]\n"
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]
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}
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],
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"source": [
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"print(my_stack.pop())\n",
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"print(my_stack.pop())\n",
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"print(my_stack)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Stack using List with a Wrapper Class\n",
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"We create a Stack class and a full set of Stack methods. \n",
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"But the underlying data structure is really a Python List. \n",
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"For pop and peek methods we first check whether the stack is empty, to avoid exceptions."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {},
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"outputs": [],
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"source": [
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"class Stack():\n",
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" def __init__(self):\n",
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" self.stack = list()\n",
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" def push(self, item):\n",
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" self.stack.append(item)\n",
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" def pop(self):\n",
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" if len(self.stack) > 0:\n",
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" return self.stack.pop()\n",
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" else:\n",
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" return None\n",
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" def peek(self):\n",
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" if len(self.stack) > 0:\n",
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" return self.stack[len(self.stack)-1]\n",
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" else:\n",
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" return None\n",
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" def __str__(self):\n",
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" return str(self.stack)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Test Code for Stack Wrapper Class"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"[1, 3]\n",
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"3\n",
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"1\n",
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"1\n",
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"None\n"
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]
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}
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],
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"source": [
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"my_stack = Stack()\n",
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"my_stack.push(1)\n",
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"my_stack.push(3)\n",
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"print(my_stack)\n",
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"print(my_stack.pop())\n",
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"print(my_stack.peek())\n",
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"print(my_stack.pop())\n",
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"print(my_stack.pop())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"---\n",
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"### Queue using Python Deque\n",
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"Queue is a FIFO data structure -- first-in, first-out. \n",
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"Deque is a double-ended queue, but we can use it for our queue. \n",
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"We use append() to enqueue an item, and popleft() to dequeue an item. \n",
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"See [Python docs](https://docs.python.org/3/library/collections.html#collections.deque) for deque."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"deque([5, 10])\n",
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"5\n"
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]
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}
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],
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"source": [
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"from collections import deque\n",
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"my_queue = deque()\n",
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"my_queue.append(5)\n",
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"my_queue.append(10)\n",
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"print(my_queue)\n",
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"print(my_queue.popleft())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Fun exercise:\n",
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"Write a wrapper class for the Queue class, similar to what we did for Stack, but using Python deque. \n",
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"Try adding enqueue, dequeue, and get_size methods."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Python Single-ended Queue Wrapper Class using Deque\n",
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"We rename the append method to enqueue, and popleft to dequeue. \n",
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"We also add peek and get_size operations."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [],
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"source": [
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"from collections import deque\n",
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"class Queue():\n",
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" def __init__(self):\n",
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" self.queue = deque()\n",
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" self.size = 0\n",
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" def enqueue(self, item):\n",
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" self.queue.append(item)\n",
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" self.size += 1\n",
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" def dequeue(self, item):\n",
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" if self.size > 0:\n",
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" self.size -= 1\n",
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" return self.queue.popleft()\n",
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" else: \n",
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" return None\n",
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" def peek(self):\n",
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" if self.size > 0:\n",
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" ret_val = self.queue.popleft()\n",
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" queue.appendleft(ret_val)\n",
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" return ret_val\n",
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" else:\n",
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" return None\n",
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" def get_size(self):\n",
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" return self.size"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Python MaxHeap\n",
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"A MaxHeap always bubbles the highest value to the top, so it can be removed instantly. \n",
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"Public functions: push, peek, pop \n",
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"Private functions: __swap, __floatUp, __bubbleDown, __str__."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 11,
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"metadata": {},
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"outputs": [],
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"source": [
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"class MaxHeap:\n",
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" def __init__(self, items=[]):\n",
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" super().__init__()\n",
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" self.heap = [0]\n",
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" for item in items:\n",
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" self.heap.append(item)\n",
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" self.__floatUp(len(self.heap) - 1)\n",
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"\n",
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" def push(self, data):\n",
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" self.heap.append(data)\n",
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" self.__floatUp(len(self.heap) - 1)\n",
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"\n",
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" def peek(self):\n",
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" if self.heap[1]:\n",
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" return self.heap[1]\n",
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" else:\n",
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" return False\n",
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" \n",
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" def pop(self):\n",
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" if len(self.heap) > 2:\n",
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" self.__swap(1, len(self.heap) - 1)\n",
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" max = self.heap.pop()\n",
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" self.__bubbleDown(1)\n",
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" elif len(self.heap) == 2:\n",
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" max = self.heap.pop()\n",
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" else: \n",
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" max = False\n",
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" return max\n",
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"\n",
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" def __swap(self, i, j):\n",
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" self.heap[i], self.heap[j] = self.heap[j], self.heap[i]\n",
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"\n",
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" def __floatUp(self, index):\n",
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" parent = index//2\n",
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" if index <= 1:\n",
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" return\n",
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" elif self.heap[index] > self.heap[parent]:\n",
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" self.__swap(index, parent)\n",
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" self.__floatUp(parent)\n",
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"\n",
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" def __bubbleDown(self, index):\n",
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" left = index * 2\n",
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" right = index * 2 + 1\n",
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" largest = index\n",
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" if len(self.heap) > left and self.heap[largest] < self.heap[left]:\n",
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" largest = left\n",
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" if len(self.heap) > right and self.heap[largest] < self.heap[right]:\n",
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" largest = right\n",
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" if largest != index:\n",
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" self.__swap(index, largest)\n",
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" self.__bubbleDown(largest)\n",
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" \n",
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" def __str__(self):\n",
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" return str(self.heap)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### MaxHeap Test Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 12,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"[0, 95, 10, 21, 3]\n",
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"95\n",
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"21\n"
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]
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}
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],
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"source": [
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"m = MaxHeap([95, 3, 21])\n",
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"m.push(10)\n",
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"print(m)\n",
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"print(m.pop())\n",
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"print(m.peek())"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.7.0"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}
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