stacks using lists-example-reverse a list

Author: ostad-ai

README.md

@@ -3,4 +3,5 @@
 1) Lists: Introduction
 2) Lists: Example, computing Khayyam-Pascal's triangle
 3) Lists: Copying
-4) Exercise: Solving quadratic equation
+4) Exercise: Solving quadratic equation
+5) Stacks are implemented by lists. An example to reverse a list with stack is also included.

stack-using a list-reverse a list with stack.ipynb

@@ -0,0 +1,182 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Python: Everything\n",
+    "- 5) Stack: Using lists in python as stacks, with an example to reverse a list\n",
+    "<br>----------------------------------------------\n",
+    "<br> By Hamed Shah-Hosseini\n",
+    "<br> https://github.com/ostad-ai/Python-Everything"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**Stack:** A linear data structure which uses two functions *push* and *pop*. \n",
+    "- The *push* adds the item at the top of stack\n",
+    "- The *pop*, returns the item at the top of stack and removes it from stack."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The stack after three pushes: ['hello', 'world', 'bye']\n"
+     ]
+    }
+   ],
+   "source": [
+    "mystack=[] #define an empty stack as a list\n",
+    "# to push items into stack\n",
+    "mystack.append('hello')\n",
+    "mystack.append('world')\n",
+    "mystack.append('bye')\n",
+    "print('The stack after three pushes:',mystack)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The stack before the pop: ['hello', 'world', 'bye']\n",
+      "The item at top: bye\n",
+      "The stack after the pop: ['hello', 'world']\n"
+     ]
+    }
+   ],
+   "source": [
+    "# the last item is the the first to pop: Last-in First-out\n",
+    "print('The stack before the pop:',mystack)\n",
+    "item_at_top=mystack.pop()\n",
+    "print('The item at top:',item_at_top)\n",
+    "print('The stack after the pop:',mystack)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 19,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Original list: [1, 2, 3, 4, 5, 6]\n",
+      "Reversed list: [6, 5, 4, 3, 2, 1]\n"
+     ]
+    }
+   ],
+   "source": [
+    "# to reverse a list by stack\n",
+    "mylist=[1,2,3,4,5,6]\n",
+    "#---to push item into stack, use append\n",
+    "#---to pop item from stack, use pop\n",
+    "stack=[]\n",
+    "mylist2=[]\n",
+    "for item in mylist:\n",
+    "    stack.append(item)\n",
+    "for i in range(len(stack)):\n",
+    "    mylist2.append(stack.pop())\n",
+    "#---print lists\n",
+    "print('Original list:',mylist)\n",
+    "print('Reversed list:',mylist2)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**Hint:** We could use *reverse* to reverse a list in place:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Original list is revered:  [6, 5, 4, 3, 2, 1]\n"
+     ]
+    }
+   ],
+   "source": [
+    "mylist=[1,2,3,4,5,6]\n",
+    "mylist.reverse() #in-place reverse\n",
+    "print('Original list is revered: ',mylist)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**Hint:** Another way to reverse a list:\n",
+    "<br>The original list does not change"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Original list: [1, 2, 3, 4, 5, 6]\n",
+      "Reversed list: [6, 5, 4, 3, 2, 1]\n"
+     ]
+    }
+   ],
+   "source": [
+    "mylist=[1,2,3,4,5,6]\n",
+    "mylist2=mylist[::-1]\n",
+    "print('Original list:',mylist)\n",
+    "print('Reversed list:',mylist2)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}