leetcode/notebooks/collections/deque.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Deque"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 84,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import deque"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Deque stands for double-ended queue. Can be used for fast, O(1) FIFO/LIFO. Internally implemented using doubly-linked lists of fixed-length blocks.\n",
    "\n",
    "Deques can be created from another sequence."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 85,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a\n",
      "g\n"
     ]
    }
   ],
   "source": [
    "d = deque('abcdefg')\n",
    "\n",
    "print(d[0])\n",
    "print(d[-1])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can extend a deque instance with another sequence either at the end or beginning"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 86,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "deque(['x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'])\n"
     ]
    }
   ],
   "source": [
    "d.extend('hij')\n",
    "d.extendleft('zyx')\n",
    "\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 87,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "deque(['w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k'])\n"
     ]
    }
   ],
   "source": [
    "d.append('k')\n",
    "d.appendleft('w')\n",
    "\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Can remove items from either ends using `pop` and `popleft`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 88,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Popped rightmost item: d\n",
      "Popped left most item: a\n"
     ]
    }
   ],
   "source": [
    "d = deque('abcd')\n",
    "\n",
    "print(\"Popped rightmost item:\", d.pop())\n",
    "print(\"Popped left most item:\", d.popleft())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Identical items can be removed using `.remove()`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 89,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "deque(['b', 'c', 'd'])\n"
     ]
    }
   ],
   "source": [
    "d = deque('abcd')\n",
    "\n",
    "d.remove('a')\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Raises `IndexError` if nothing left to remove"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 90,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "d c b a "
     ]
    }
   ],
   "source": [
    "s = deque('abcd')\n",
    "\n",
    "while True:\n",
    "    try:\n",
    "        print(s.pop(), end=\" \")\n",
    "    except IndexError:\n",
    "        break"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "⭐️ Rotate a given collection"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 91,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "deque(['c', 'd', 'a', 'b'])\n",
      "deque(['a', 'b', 'c', 'd'])\n"
     ]
    }
   ],
   "source": [
    "d = deque('abcd')\n",
    "\n",
    "d.rotate(2)\n",
    "print(d)\n",
    "\n",
    "d.rotate(-2)\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "⭐️ Deque size can be constrained using `maxlen`. Useful when dealing with streams of values but we just need to keep latest `n` items"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 92,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Left deque: deque([4, 3, 2], maxlen=3)\n",
      "Right deque: deque([2, 3, 4], maxlen=3)\n"
     ]
    }
   ],
   "source": [
    "import random\n",
    "\n",
    "ld = deque(maxlen=3)\n",
    "rd = deque(maxlen=3)\n",
    "\n",
    "for i in range(5):\n",
    "    ld.appendleft(i)\n",
    "    rd.append(i)\n",
    "\n",
    "print(\"Left deque:\", ld)\n",
    "print(\"Right deque:\", rd)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Deque is thread-safe, so can be consumed from both ends at same-time."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 96,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "    Left: 0\n",
      "   Right: 4\n",
      "    Left: 1\n",
      "   Right: 3\n",
      "    Left: 2\n",
      "   Right: Done\n",
      "    Left: Done\n"
     ]
    }
   ],
   "source": [
    "import threading\n",
    "import time\n",
    "\n",
    "items = deque(range(5))\n",
    "\n",
    "def consume(direction, get_next):\n",
    "    while True:\n",
    "        try:\n",
    "            next = get_next()\n",
    "            print(f\"{direction:>8}: {next}\")\n",
    "            time.sleep(0.1)\n",
    "        except IndexError:\n",
    "            break\n",
    "    \n",
    "    print(f\"{direction:>8}: Done\")\n",
    "\n",
    "left = threading.Thread(target=consume, args=('Left', items.popleft))\n",
    "right = threading.Thread(target=consume, args=('Right', items.pop))\n",
    "\n",
    "left.start()\n",
    "right.start()\n",
    "\n",
    "left.join()\n",
    "right.join()\n"
   ]
  }
 ],
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