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Adding postfix stack application #21

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Adding postfix stack application #21

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ef5a26a
Created using Colaboratory
EdaYeo Oct 15, 2020
37f370d
Update Python15_Stack.ipynb
EdaYeo Jan 20, 2022
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398 changes: 398 additions & 0 deletions Python15_Stack.ipynb
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Original file line number Diff line number Diff line change
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{
"nbformat": 4,
"nbformat_minor": 0,
"metadata": {
"colab": {
"name": "Python15 - Stack.ipynb",
"provenance": [],
"include_colab_link": true
},
"kernelspec": {
"name": "python3",
"display_name": "Python 3"
}
},
"cells": [
{
"cell_type": "markdown",
"metadata": {
"id": "view-in-github",
"colab_type": "text"
},
"source": [
"<a href=\"https://colab.research.google.com/github/killuen/cp4all/blob/main/Python15_Stack.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>"
]
},
{
"cell_type": "markdown",
"metadata": {
"id": "WYDSZcGSKwqH"
},
"source": [
"# Stack\n",
"- last in first out (LIFO) data structure\n",
"- essential data: data, top\n",
"- top is the position when the next item will be inserted or removed\n",
"- can be implemented using array or linked list"
]
},
{
"cell_type": "code",
"metadata": {
"id": "RgRsqtYFKrH0",
"outputId": "cae94c74-de91-44d8-a25e-95121205d2a7",
"colab": {
"base_uri": "https://localhost:8080/",
"height": 158
}
},
"source": [
"# Stack class\n",
"class Stack:\n",
"\n",
" def __init__(self): # encapsulation\n",
" self.data = []\n",
" self.top = -1 # assume/take -1 to be invalid index\n",
"\n",
" def is_empty(self):\n",
" return self.top == -1\n",
"\n",
" def push(self, value): # insert\n",
" self.top = 0\n",
" self.data.insert(0, value)\n",
" print(value, \"inserted\")\n",
"\n",
" def pop(self): # delete\n",
" if self.is_empty():\n",
" print(\"Cannot delete from empty stack\")\n",
" return -1 # signify error\n",
" else:\n",
" value = self.data[self.top]\n",
" del self.data[self.top]\n",
" #print(value, \"deleted\")\n",
" if len(self.data) == 0:\n",
" self.top = -1\n",
" return value\n",
"\n",
" def peek(self): # return top item without removing it\n",
" if self.is_empty():\n",
" return \"Empty stack\"\n",
" else:\n",
" return self.data[self.top]\n",
"\n",
" def display(self):\n",
" if self.is_empty():\n",
" print(\"Empty stack\")\n",
" else:\n",
" print(\"Contents: \", end='')\n",
" for item in self.data:\n",
" print(item, end=' ')\n",
" print()\n",
"\n",
"# main\n",
"stack = Stack()\n",
"stack.push(35)\n",
"stack.push(88)\n",
"stack.push(19)\n",
"#print(stack.data, stack.top)\n",
"stack.display()\n",
"stack.pop()\n",
"stack.display()\n",
"print(stack.peek())\n",
"stack.pop()\n",
"stack.pop()\n",
"stack.pop()\n",
"stack.display()"
],
"execution_count": null,
"outputs": [
{
"output_type": "stream",
"text": [
"35 inserted\n",
"88 inserted\n",
"19 inserted\n",
"Contents: 19 88 35 \n",
"Contents: 88 35 \n",
"88\n",
"Cannot delete from empty stack\n",
"Empty stack\n"
],
"name": "stdout"
}
]
},
{
"cell_type": "markdown",
"metadata": {
"id": "xZnIB3u5jMmL"
},
"source": [
"Implement stack using append instead of insert"
]
},
{
"cell_type": "code",
"metadata": {
"id": "5r8vGR4Ga0Cj",
"outputId": "04049849-ce0d-4f50-c4f5-3ed9a815a6f7",
"colab": {
"base_uri": "https://localhost:8080/",
"height": 84
}
},
"source": [
"class Stack:\n",
"\n",
" def __init__(self):\n",
" self.data = []\n",
"\n",
" def is_empty(self):\n",
" return len(self.data) == 0 # self.data == []\n",
"\n",
" def push(self, value): # insert\n",
" self.data.append(value)\n",
"\n",
" def pop(self): # delete\n",
" if self.is_empty():\n",
" return \"Cannot delete from empty stack\"\n",
" return self.data.pop()\n",
"\n",
" def peek(self):\n",
" return self.data[len(self.data)-1] # self.data[-1]\n",
"\n",
" def size(self):\n",
" return len(self.data)\n",
"\n",
" def display(self):\n",
" if self.is_empty():\n",
" print(\"Empty stack\")\n",
" else:\n",
" print(\"Contents: \", end='')\n",
" for i in range(len(self.data)):\n",
" print(self.data[i], end=' ')\n",
" print()\n",
"\n",
"\n",
"# main\n",
"stack = Stack()\n",
"stack.push(35)\n",
"stack.push(88)\n",
"stack.push(19)\n",
"#print(stack.data, stack.top)\n",
"stack.display()\n",
"stack.pop()\n",
"stack.display()\n",
"print(stack.peek())\n",
"stack.pop()\n",
"stack.pop()\n",
"stack.pop()\n",
"stack.display()"
],
"execution_count": null,
"outputs": [
{
"output_type": "stream",
"text": [
"Contents: 35 88 19 \n",
"Contents: 35 88 \n",
"88\n",
"Empty stack\n"
],
"name": "stdout"
}
]
},
{
"cell_type": "code",
"metadata": {
"id": "3RQ4PGggc6sH",
"outputId": "59ed5874-503d-4efc-e098-dde36820d5be",
"colab": {
"base_uri": "https://localhost:8080/",
"height": 191
}
},
"source": [
"# Stack application - reverse\n",
"#items = 'stressed'\n",
"items = list('stressed')\n",
"print(items)\n",
"s = Stack()\n",
"for item in items:\n",
" s.push(item)\n",
"for i in range(len(s.data)):\n",
" print(s.pop(), end='')"
],
"execution_count": null,
"outputs": [
{
"output_type": "stream",
"text": [
"['s', 't', 'r', 'e', 's', 's', 'e', 'd']\n",
"s inserted\n",
"t inserted\n",
"r inserted\n",
"e inserted\n",
"s inserted\n",
"s inserted\n",
"e inserted\n",
"d inserted\n",
"desserts"
],
"name": "stdout"
}
]
},
{
"cell_type": "markdown",
"metadata": {
"id": "J2suTbJtjZeX"
},
"source": [
"35 // 2 = 17 r 1\n",
"\n",
"17 // 2 = 8 r 1\n",
"\n",
"8 // 2 = 4 r 0\n",
"\n",
"4 // 2 = 2 r 0\n",
"\n",
"2 // 2 = 1 r 0\n",
"\n",
"1\n",
"\n",
"35 = 100011"
]
},
{
"cell_type": "code",
"metadata": {
"id": "ufT0KeA1c9ZR",
"outputId": "a378c655-38b7-4680-8cb2-8f4354db51f5",
"colab": {
"base_uri": "https://localhost:8080/",
"height": 121
}
},
"source": [
"# Stack application - decimal to binary conversion\n",
"dec = 35\n",
"s = Stack()\n",
"while dec >= 2:\n",
" rem = dec % 2\n",
" s.push(rem)\n",
" dec //= 2 # dec = dec // 2\n",
"print(1, end='')\n",
"while not s.is_empty():\n",
" print(s.pop(), end='')"
],
"execution_count": null,
"outputs": [
{
"output_type": "stream",
"text": [
"1 inserted\n",
"1 inserted\n",
"0 inserted\n",
"0 inserted\n",
"0 inserted\n",
"100011"
],
"name": "stdout"
}
]
},
{
"cell_type": "code",
"metadata": {
"id": "ZeBmJh0ykq9h"
},
"source": [
"# Stack application - check balanced expression\n",
"expr = '(2 + 3) * 4'"
],
"execution_count": null,
"outputs": []
},
{
"cell_type": "code",
"metadata": {
"id": "ACko8RHWp5E0",
"outputId": "cd30daba-ad40-40cd-b344-3301bcf2296d",
"colab": {
"base_uri": "https://localhost:8080/",
"height": 283
}
},
"source": [
"# Stack application - calculating postfix\n",
"postfix = \"231+*5-\"\n",
"pfl = []\n",
"stack = Stack()\n",
"for i in range(len(postfix)):\n",
" pfl.append(postfix[i])\n",
"\n",
"j = 0\n",
"for i in range(len(pfl)):\n",
" if pfl[i].isdigit():\n",
" stack.push(int(pfl[i]))\n",
" else:\n",
" num2, num1 = stack.pop(), stack.pop()\n",
"\n",
" result = 0\n",
" if pfl[i] == \"+\":\n",
" result = num1 + num2\n",
"\n",
" if pfl[i] == \"-\":\n",
" result = num1 - num2\n",
"\n",
" if pfl[i] == \"*\":\n",
" result = num1 * num2\n",
"\n",
" if pfl[i] == \"/\":\n",
" result = num1 / num2\n",
"\n",
" stack.push(result)\n",
" stack.display()\n",
"\n",
"stack.display()"
],
"execution_count": null,
"outputs": [
{
"output_type": "stream",
"text": [
"2 inserted\n",
"Contents: 2 \n",
"3 inserted\n",
"Contents: 3 2 \n",
"1 inserted\n",
"Contents: 1 3 2 \n",
"4 inserted\n",
"Contents: 4 2 \n",
"8 inserted\n",
"Contents: 8 \n",
"5 inserted\n",
"Contents: 5 8 \n",
"3 inserted\n",
"Contents: 3 \n",
"Contents: 3 \n"
],
"name": "stdout"
}
]
},
{
"cell_type": "code",
"metadata": {
"id": "gDCbnB3Bp8Qj"
},
"source": [
""
],
"execution_count": null,
"outputs": []
}
]
}
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