From fc9de925a1bf76dc89872d2e1d6a3398dc79dae3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bertalan=20K=C3=B6rmendy?= Date: Thu, 19 Jul 2018 15:43:40 +0200 Subject: [PATCH] added some edge cases and dunder methods --- README.md | 2 +- .../circular_array/circular_array.ipynb | 128 ++++++++++++++++++ 2 files changed, 129 insertions(+), 1 deletion(-) create mode 100644 solutions/object_oriented_design/circular_array/circular_array.ipynb diff --git a/README.md b/README.md index fd894e4e..37750f72 100644 --- a/README.md +++ b/README.md @@ -362,7 +362,7 @@ Check out the following links to get a better idea of what to expect: | Design a deck of cards | [Solution](solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb) | | Design a parking lot | [Solution](solutions/object_oriented_design/parking_lot/parking_lot.ipynb) | | Design a chat server | [Solution](solutions/object_oriented_design/online_chat/online_chat.ipynb) | -| Design a circular array | [Contribute](#contributing) | +| Design a circular array | [Solution](solutions/object_oriented_design/circular_array/circular_array.ipynb) | | Add an object-oriented design question | [Contribute](#contributing) | ## System design topics: start here diff --git a/solutions/object_oriented_design/circular_array/circular_array.ipynb b/solutions/object_oriented_design/circular_array/circular_array.ipynb new file mode 100644 index 00000000..6b3dca99 --- /dev/null +++ b/solutions/object_oriented_design/circular_array/circular_array.ipynb @@ -0,0 +1,128 @@ +{ + "cells": [ + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Constraints and Assumptions\n", + "> Can we assume the list fits in memory?\n", + "\n", + "Yes\n", + "\n", + "> Do we have to worry about load factors?\n", + "\n", + "No" + ] + }, + { + "cell_type": "code", + "execution_count": 131, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "class CircularArray:\n", + " \"\"\"\n", + " Python class implementing a circular array.\n", + " Credits to Sarath S. Pillai for some edge cases (https://github.com/sarathsp06)\n", + " \"\"\"\n", + " def __init__(self, size):\n", + " \"\"\"\n", + " Constructor. Refer to `full()` for explanation for `size+1`.\n", + " \"\"\"\n", + " if (size < 0):\n", + " raise RuntimeError(\"Invalid size (smaller than zero)\")\n", + " self._size = size + 1\n", + " self._items = [None for _ in range(self._size)]\n", + " self._read = 0 # read pointer (head of list)\n", + " self._write = 0 # write pointer (tail of list)\n", + " \n", + " def __len__(self):\n", + " '''\n", + " Returns how many elements are in the array.\n", + " '''\n", + " return (self._write - self._read) % (self._size - 1)\n", + " \n", + " def __getitem__(self, index):\n", + " if index < 0:\n", + " raise IndexError(\"Key must be a positive interger\")\n", + " if index > len(self):\n", + " raise IndexError(\"Index out of range\")\n", + " return self._items[((self._read + key) % self._size)]\n", + " \n", + " def __repr__(self):\n", + " if self.empty:\n", + " return \"\"\n", + " if self._read < self._write:\n", + " return \"\".format(self._items[self._read:self._write])\n", + " return \"\".format(self._items[self._read:] + self._items[:self._write])\n", + " \n", + " @property\n", + " def capacity(self):\n", + " return self._size - 1\n", + " \n", + " @property\n", + " def empty(self):\n", + " \"\"\"\n", + " Returns whether the queue is empty.\n", + " \"\"\"\n", + " return self._read == self._write\n", + " \n", + " @property\n", + " def full(self):\n", + " \"\"\"\n", + " Returns wheter the queue is full.\n", + " In a naive implementation, full and empty are both indicated by read == write, which introduces an\n", + " ambiguity. Thus, to break this, a circular array is assumed to be full if the write pointer is one\n", + " position behind the read pointer. To preserve the inituitiveness of the class interface, the internal\n", + " size property is incremented by 1, a sentinel element (so this way the user won't be surprised that their\n", + " array that supposedly fits 10 elements only accomodates 9).\n", + " \"\"\"\n", + " return self._read == (self._write + 1) % self._size\n", + " \n", + " def queue(self, item):\n", + " \"\"\"\n", + " Enqueues an item in the circular buffer.\n", + " \"\"\"\n", + " if self.full:\n", + " raise BufferError('Queue is full')\n", + " self._items[self._write] = item\n", + " self._write = (self._write + 1) % self._size\n", + " \n", + " def dequeue(self):\n", + " \"\"\"\n", + " Dequeues an item from the buffer.\n", + " \"\"\"\n", + " if self.empty:\n", + " raise BufferError('Queue is empty')\n", + " item = self._items[self._read]\n", + " self._items[self._read] = None\n", + " self._read = (self._read + 1) % self._size\n", + " return item" + ] + } + ], + "metadata": { + "anaconda-cloud": {}, + "kernelspec": { + "display_name": "Python [py35]", + "language": "python", + "name": "Python [py35]" + }, + "language_info": { + "codemirror_mode": { + "name": "ipython", + "version": 3 + }, + "file_extension": ".py", + "mimetype": "text/x-python", + "name": "python", + "nbconvert_exporter": "python", + "pygments_lexer": "ipython3", + "version": "3.5.1" + } + }, + "nbformat": 4, + "nbformat_minor": 0 +}