mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
synced 2024-03-22 13:11:13 +08:00
Added notebook solving the following: Find the start of a linked list loop.
This commit is contained in:
Donne Martin
parent
db47e1bcaa
commit
e5d7fbfe0f
|
|
@ -27,6 +27,7 @@ Continually updated IPython Notebooks containing coding problems and solutions (
|
|||
* [Delete a node in the middle of a linked list, given access to only that node](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/linked-lists/delete-mid.ipynb)
|
||||
* [Partition a linked list around a given value](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/linked-lists/partition.ipynb)
|
||||
* [Add two numbers whose digits are stored in a linked list in reverse order](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/linked-lists/add-reverse.ipynb)
|
||||
* [Find the start of a linked list loop](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/linked-lists/find-loop-start.ipynb)
|
||||
|
||||
## Stacks and Queues
|
||||
|
||||
|
|
|
|||
177
linked-lists/find-loop-start.ipynb
Normal file
177
linked-lists/find-loop-start.ipynb
Normal file
|
|
@ -0,0 +1,177 @@
|
|||
{
|
||||
"cells": [
|
||||
{
|
||||
"cell_type": "markdown",
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"## Problem: Find the start of a linked list loop.\n",
|
||||
"\n",
|
||||
"* [Clarifying Questions](#Clarifying-Questions)\n",
|
||||
"* [Test Cases](#Test-Cases)\n",
|
||||
"* [Algorithm](#Algorithm)\n",
|
||||
"* [Code](#Code)"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "markdown",
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"## Clarifying Questions\n",
|
||||
"\n",
|
||||
"* This is a singly linked list?\n",
|
||||
" * Yes\n",
|
||||
"* Can we assume we are always passed a circular linked list?\n",
|
||||
" * No"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "markdown",
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"## Test Cases\n",
|
||||
"\n",
|
||||
"* Empty list\n",
|
||||
"* Not a circular linked list\n",
|
||||
" * One element\n",
|
||||
" * Two elements\n",
|
||||
" * Three or more elements\n",
|
||||
"* General case"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "markdown",
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"## Algorithm\n",
|
||||
"\n",
|
||||
"* Check for an empty list\n",
|
||||
"* Use two pointers i, j, initialized to the head\n",
|
||||
"* j is incremented twice as fast as i\n",
|
||||
" * If j's next is NULL, we do not have a circular list\n",
|
||||
"* When i and j meet, move j to the head\n",
|
||||
"* Increment i and j one node at a time until they meet\n",
|
||||
"* Where they meet is the start of the loop\n",
|
||||
"\n",
|
||||
"Complexity:\n",
|
||||
"* Time: O(n)\n",
|
||||
"* Space: In-place"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "markdown",
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"## Code"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "code",
|
||||
"execution_count": null,
|
||||
"metadata": {
|
||||
"collapsed": true
|
||||
},
|
||||
"outputs": [],
|
||||
"source": [
|
||||
"%run linked_list.py"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "code",
|
||||
"execution_count": null,
|
||||
"metadata": {
|
||||
"collapsed": false
|
||||
},
|
||||
"outputs": [],
|
||||
"source": [
|
||||
"class MyLinkedList(LinkedList):\n",
|
||||
" def find_loop_start(self):\n",
|
||||
" if self.head is None or self.head.next is None:\n",
|
||||
" return\n",
|
||||
" i = self.head\n",
|
||||
" j = self.head\n",
|
||||
" i = i.next\n",
|
||||
" j = j.next.next\n",
|
||||
" while j != i:\n",
|
||||
" i = i.next\n",
|
||||
" if j is None or j.next is None:\n",
|
||||
" return\n",
|
||||
" j = j.next.next\n",
|
||||
" j = self.head\n",
|
||||
" while j != i:\n",
|
||||
" i = i.next\n",
|
||||
" j = j.next\n",
|
||||
" return i.data"
|
||||
]
|
||||
},
|
||||
{
|
||||
"cell_type": "code",
|
||||
"execution_count": null,
|
||||
"metadata": {
|
||||
"collapsed": false
|
||||
},
|
||||
"outputs": [],
|
||||
"source": [
|
||||
"print('Empty list')\n",
|
||||
"linked_list = MyLinkedList()\n",
|
||||
"print(linked_list.find_loop_start())\n",
|
||||
"print('Not a circular linked list')\n",
|
||||
"print('One element')\n",
|
||||
"head = Node(1)\n",
|
||||
"linked_list = MyLinkedList(head)\n",
|
||||
"print(linked_list.find_loop_start())\n",
|
||||
"print('Two elements')\n",
|
||||
"linked_list.append(2)\n",
|
||||
"print(linked_list.find_loop_start())\n",
|
||||
"print('Three or more elements')\n",
|
||||
"linked_list.append(3)\n",
|
||||
"print(linked_list.find_loop_start())\n",
|
||||
"print('General case')\n",
|
||||
"node0 = Node(0)\n",
|
||||
"node1 = Node(1)\n",
|
||||
"node2 = Node(2)\n",
|
||||
"node3 = Node(3)\n",
|
||||
"node4 = Node(4)\n",
|
||||
"node5 = Node(5)\n",
|
||||
"node6 = Node(6)\n",
|
||||
"node7 = Node(7)\n",
|
||||
"node8 = Node(8)\n",
|
||||
"node9 = Node(9)\n",
|
||||
"node10 = Node(10)\n",
|
||||
"node0.next = node1\n",
|
||||
"node1.next = node2\n",
|
||||
"node2.next = node3\n",
|
||||
"node3.next = node4\n",
|
||||
"node4.next = node5\n",
|
||||
"node5.next = node6\n",
|
||||
"node6.next = node7\n",
|
||||
"node7.next = node8\n",
|
||||
"node8.next = node9\n",
|
||||
"node9.next = node10\n",
|
||||
"node10.next = node3\n",
|
||||
"linked_list = MyLinkedList(node0)\n",
|
||||
"print(linked_list.find_loop_start())"
|
||||
]
|
||||
}
|
||||
],
|
||||
"metadata": {
|
||||
"kernelspec": {
|
||||
"display_name": "Python 2",
|
||||
"language": "python",
|
||||
"name": "python2"
|
||||
},
|
||||
"language_info": {
|
||||
"codemirror_mode": {
|
||||
"name": "ipython",
|
||||
"version": 2
|
||||
},
|
||||
"file_extension": ".py",
|
||||
"mimetype": "text/x-python",
|
||||
"name": "python",
|
||||
"nbconvert_exporter": "python",
|
||||
"pygments_lexer": "ipython2",
|
||||
"version": "2.7.9"
|
||||
}
|
||||
},
|
||||
"nbformat": 4,
|
||||
"nbformat_minor": 0
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user