106 lines
3.2 KiB
Python
106 lines
3.2 KiB
Python
{
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"cells": [
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{
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"cell_type": "markdown",
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"source": [
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"## Constraints and Assumptions\n",
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"> Can we assume the list fits in memory?\n",
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"\n",
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"Yes\n",
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"\n",
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"> Do we have to worry about load factors?\n",
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"\n",
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"No\n",
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"\n",
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"> Can we assume inputs are valid or do we have to validate them?\n",
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"\n",
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"Assume they are valid"
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]
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"cell_type": "code",
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"class CircularArray:\n",
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" \"\"\"\n",
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" Python class implementing a circular array.\n",
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" \"\"\"\n",
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" def __init__(self, size):\n",
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" \"\"\"\n",
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" Constructor. Refer to `full()` for explanation for `size+1`.\n",
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" \"\"\"\n",
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" self._size = size + 1\n",
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" self._items = [None for _ in range(self._size)]\n",
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" self._read = 0 # read pointer\n",
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" self._write = 0 # write pointer\n",
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" \n",
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" @property\n",
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" def empty(self):\n",
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" \"\"\"\n",
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" Returns whether the queue is empty.\n",
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" \"\"\"\n",
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" return self._read == self._write\n",
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" \n",
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" @property\n",
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" def full(self):\n",
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" \"\"\"\n",
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" Return wheter the queue is full.\n",
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" In a naive implementation, full and empty are both indicated by read == write, which introduces an\n",
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" ambiguity. Thus, to break this, a circular array is assumed to be full if the write pointer is one\n",
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" position behind the read pointer. To preserve the inituitiveness of the class interface, the internal\n",
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" size property is incremented by 1, a sentinel element (so this way the user won't be surprised that their\n",
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" array that supposedly fits 10 elements only accomodates 9).\n",
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" \"\"\"\n",
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" return self._read == (self._write + 1) % self._size\n",
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" \n",
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" def queue(self, item):\n",
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" \"\"\"\n",
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" Enqueues an item in the circular buffer.\n",
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" \"\"\"\n",
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" if self.full:\n",
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" raise BufferError('Queue is full')\n",
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" self._items[self._write] = item\n",
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" self._write = (self._write + 1) % self._size\n",
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" \n",
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" def dequeue(self):\n",
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" \"\"\"\n",
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" Dequeues an item from the buffer.\n",
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" \"\"\"\n",
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" if self.empty:\n",
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" raise BufferError('Queue is empty')\n",
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" item = self._items[self._read]\n",
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" self._items[self._read] = None\n",
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" self._read = (self._read + 1) % self._size\n",
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" return item"
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]
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}
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],
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"display_name": "Python [py35]",
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"language": "python",
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"name": "Python [py35]"
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.1"
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