{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Radix Sort\n",
    "(c) 2020, Joe James"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "# get number of digits in largest item\n",
    "def __get_num_digits(A):\n",
    "    m = 0\n",
    "    for item in A:\n",
    "        m = max(m, item)\n",
    "    return len(str(m))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "# flatten into a 1D List\n",
    "from functools import reduce\n",
    "def __flatten(A):\n",
    "    return reduce(lambda x, y: x + y, A)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Changed from YouTube video:\n",
    "It's much cleaner to put the _get_num_digits call inside the radix function rather than in main as shown in the video. That way you only need to pass a List to the radix function. Thanks to Brother Lui for this suggestion."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "def radix(A):\n",
    "    num_digits = __get_num_digits(A)\n",
    "    for digit in range(0, num_digits):\n",
    "        B = [[] for i in range(10)]\n",
    "        for item in A:\n",
    "            # num is the bucket number that the item will be put into\n",
    "            num = item // 10 ** (digit) % 10\n",
    "            B[num].append(item)\n",
    "        A = __flatten(B)\n",
    "    return A"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 45, 53, 55, 213, 288, 289]\n",
      "[0, 1, 2, 3, 4, 5] [999994, 999995, 999996, 999997, 999998, 999999]\n"
     ]
    }
   ],
   "source": [
    "def main():\n",
    "    A = [55, 45, 3, 289, 213, 1, 288, 53, 2]\n",
    "    A = radix(A)\n",
    "    print(A)\n",
    "    \n",
    "    B  = [i for i in range(1000000)]\n",
    "    from random import shuffle\n",
    "    shuffle(B)\n",
    "    B = radix(B)\n",
    "    print(B[:6], B[-6:])\n",
    "\n",
    "main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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