|
| 1 | +{ |
| 2 | + "cells": [ |
| 3 | + { |
| 4 | + "cell_type": "markdown", |
| 5 | + "metadata": {}, |
| 6 | + "source": [ |
| 7 | + "## Singly Linked Lists\n", |
| 8 | + "It is a collection of nodes. Each node has an element and a reference to the next node in the collections. **HEAD** is a member that points to the first node in the collection. The last node is called **TAIL**. The last node is has a reference to *None*. Traversing a linked list is also called **link hopping** or **pointer hopping**.\n", |
| 9 | + "\n", |
| 10 | + "An important property of a linked list is it does not have a predefined fixed size.\n", |
| 11 | + "To insert an element to the HEAD:\n", |
| 12 | + "* create a new node with the element\n", |
| 13 | + "* new node point to head reference\n", |
| 14 | + "* head point to ne node\n", |
| 15 | + "\n", |
| 16 | + "To insert an element to the TAIL:\n", |
| 17 | + "* create a new node\n", |
| 18 | + "* tail reference points to new node\n", |
| 19 | + "* tail points to new node\n", |
| 20 | + "\n", |
| 21 | + "Removing an element from HEAD:\n", |
| 22 | + "* head points to head reference\n", |
| 23 | + "\n", |
| 24 | + "Removing an element from TAIL: not an easy task\n", |
| 25 | + "\n", |
| 26 | + "O(n) -> accessing element\n", |
| 27 | + "O(1) -> insertion and deletion of an element " |
| 28 | + ] |
| 29 | + }, |
| 30 | + { |
| 31 | + "cell_type": "code", |
| 32 | + "execution_count": 2, |
| 33 | + "metadata": {}, |
| 34 | + "outputs": [ |
| 35 | + { |
| 36 | + "name": "stdout", |
| 37 | + "output_type": "stream", |
| 38 | + "text": [ |
| 39 | + "1\n", |
| 40 | + "<__main__.Node object at 0x10c6005c0>\n", |
| 41 | + "2\n" |
| 42 | + ] |
| 43 | + } |
| 44 | + ], |
| 45 | + "source": [ |
| 46 | + "class Node(object):\n", |
| 47 | + " def __init__(self, ele):\n", |
| 48 | + " self.value = ele\n", |
| 49 | + " self.next_node = None\n", |
| 50 | + " \n", |
| 51 | + "a = Node(1)\n", |
| 52 | + "b = Node(2)\n", |
| 53 | + "c = Node(3)\n", |
| 54 | + "\n", |
| 55 | + "a.next_node = b\n", |
| 56 | + "b.next_node = c\n", |
| 57 | + "\n", |
| 58 | + "print(a.value)\n", |
| 59 | + "print(a.next_node)\n", |
| 60 | + "print(a.next_node.value)" |
| 61 | + ] |
| 62 | + }, |
| 63 | + { |
| 64 | + "cell_type": "markdown", |
| 65 | + "metadata": {}, |
| 66 | + "source": [ |
| 67 | + "## Doubly Linked List\n", |
| 68 | + "A linked list in which each node keeps a reference to the node after it as well as node before it. The *next* is used to refer to next node and *prev* to refer to previous node.\n", |
| 69 | + "\n", |
| 70 | + "A **header** node is at the beginning and a **trailer** is node is at the last. These nodes are called sentinel or dummy nodes." |
| 71 | + ] |
| 72 | + }, |
| 73 | + { |
| 74 | + "cell_type": "code", |
| 75 | + "execution_count": 5, |
| 76 | + "metadata": {}, |
| 77 | + "outputs": [ |
| 78 | + { |
| 79 | + "name": "stdout", |
| 80 | + "output_type": "stream", |
| 81 | + "text": [ |
| 82 | + "1\n" |
| 83 | + ] |
| 84 | + } |
| 85 | + ], |
| 86 | + "source": [ |
| 87 | + "class DoublyLLNode(object):\n", |
| 88 | + " def __init__(self, ele):\n", |
| 89 | + " self.prev_node = None\n", |
| 90 | + " self.value = ele\n", |
| 91 | + " self.next_node = Node\n", |
| 92 | + " \n", |
| 93 | + "a = DoublyLLNode(1)\n", |
| 94 | + "b = DoublyLLNode(2)\n", |
| 95 | + "c = DoublyLLNode(3)\n", |
| 96 | + "\n", |
| 97 | + "a.next_node = b\n", |
| 98 | + "b.prev_node = a\n", |
| 99 | + "b.next_node = c\n", |
| 100 | + "c.prev_node = b\n", |
| 101 | + "\n", |
| 102 | + "print(b.prev_node.value)" |
| 103 | + ] |
| 104 | + }, |
| 105 | + { |
| 106 | + "cell_type": "markdown", |
| 107 | + "metadata": {}, |
| 108 | + "source": [ |
| 109 | + "## Interview Questions" |
| 110 | + ] |
| 111 | + }, |
| 112 | + { |
| 113 | + "cell_type": "code", |
| 114 | + "execution_count": 12, |
| 115 | + "metadata": {}, |
| 116 | + "outputs": [ |
| 117 | + { |
| 118 | + "name": "stdout", |
| 119 | + "output_type": "stream", |
| 120 | + "text": [ |
| 121 | + "False\n", |
| 122 | + "True\n" |
| 123 | + ] |
| 124 | + } |
| 125 | + ], |
| 126 | + "source": [ |
| 127 | + "\"\"\"\n", |
| 128 | + "Singly Linked List Cycle List: check if the list has cycles\n", |
| 129 | + "\"\"\"\n", |
| 130 | + "class Node(object):\n", |
| 131 | + " def __init__(self, ele):\n", |
| 132 | + " self.value = ele\n", |
| 133 | + " self.nextnode = None\n", |
| 134 | + " \n", |
| 135 | + "def cycle_check(node):\n", |
| 136 | + " marker1 = node\n", |
| 137 | + " marker2 = node\n", |
| 138 | + " while marker2!=None and marker2.nextnode!=None:\n", |
| 139 | + " marker1 = marker1.nextnode\n", |
| 140 | + " marker2 = marker2.nextnode.nextnode\n", |
| 141 | + " if marker2 == marker1:\n", |
| 142 | + " return True\n", |
| 143 | + " return False\n", |
| 144 | + "\n", |
| 145 | + "a = Node(1)\n", |
| 146 | + "b = Node(2)\n", |
| 147 | + "c = Node(3)\n", |
| 148 | + "\n", |
| 149 | + "a.nextnode = b\n", |
| 150 | + "b.nextnode = c\n", |
| 151 | + "print(cycle_check(a))\n", |
| 152 | + "c.nextnode = a\n", |
| 153 | + "print(cycle_check(a))" |
| 154 | + ] |
| 155 | + }, |
| 156 | + { |
| 157 | + "cell_type": "code", |
| 158 | + "execution_count": null, |
| 159 | + "metadata": {}, |
| 160 | + "outputs": [], |
| 161 | + "source": [] |
| 162 | + } |
| 163 | + ], |
| 164 | + "metadata": { |
| 165 | + "kernelspec": { |
| 166 | + "display_name": "Python 3", |
| 167 | + "language": "python", |
| 168 | + "name": "python3" |
| 169 | + }, |
| 170 | + "language_info": { |
| 171 | + "codemirror_mode": { |
| 172 | + "name": "ipython", |
| 173 | + "version": 3 |
| 174 | + }, |
| 175 | + "file_extension": ".py", |
| 176 | + "mimetype": "text/x-python", |
| 177 | + "name": "python", |
| 178 | + "nbconvert_exporter": "python", |
| 179 | + "pygments_lexer": "ipython3", |
| 180 | + "version": "3.7.3" |
| 181 | + } |
| 182 | + }, |
| 183 | + "nbformat": 4, |
| 184 | + "nbformat_minor": 2 |
| 185 | +} |
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