{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python QuickSort Algorithm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[5, 9, 1, 2, 4, 8, 6, 3, 7]\n",
      "[1, 2, 3, 4, 5, 6, 7, 8, 9]\n"
     ]
    }
   ],
   "source": [
    "#---------------------------------------\n",
    "# Quick Sort\n",
    "#---------------------------------------\n",
    "def quick_sort(A):\n",
    "    quick_sort2(A, 0, len(A)-1)\n",
    "    \n",
    "def quick_sort2(A, low, hi):\n",
    "    if hi-low < 1 and low < hi:\n",
    "        quick_selection(A, low, hi)\n",
    "    elif low < hi:\n",
    "        p = partition(A, low, hi)\n",
    "        quick_sort2(A, low, p - 1)\n",
    "        quick_sort2(A, p + 1, hi)\n",
    "    \n",
    "def get_pivot(A, low, hi):\n",
    "    mid = (hi + low) // 2\n",
    "    s = sorted([A[low], A[mid], A[hi]])\n",
    "    if s[1] == A[low]:\n",
    "        return low\n",
    "    elif s[1] == A[mid]:\n",
    "        return mid\n",
    "    return hi\n",
    "    \n",
    "def partition(A, low, hi):\n",
    "    pivotIndex = get_pivot(A, low, hi)\n",
    "    pivotValue = A[pivotIndex]\n",
    "    A[pivotIndex], A[low] = A[low], A[pivotIndex]\n",
    "    border = low\n",
    "\n",
    "    for i in range(low, hi+1):\n",
    "        if A[i] < pivotValue:\n",
    "            border += 1\n",
    "            A[i], A[border] = A[border], A[i]\n",
    "    A[low], A[border] = A[border], A[low]\n",
    "\n",
    "    return (border)\n",
    "    \n",
    "def quick_selection(x, first, last):\n",
    "    for i in range (first, last):\n",
    "        minIndex = i\n",
    "        for j in range (i+1, last+1):\n",
    "            if x[j] < x[minIndex]:\n",
    "                minIndex = j\n",
    "        if minIndex != i:\n",
    "            x[i], x[minIndex] = x[minIndex], x[i]\n",
    "            \n",
    "A = [5,9,1,2,4,8,6,3,7]\n",
    "print(A)\n",
    "quick_sort(A)\n",
    "print(A)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Nice simple version written by Mr. UncleChu in comments\n",
    "Slick code, but does not sort in place, so uses a lot more memory. Do not use for large lists or you'll get stackoverflow."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[5, 9, 1, 2, 4, 8, 6, 3, 7]\n",
      "[1, 2, 3, 4, 5, 6, 7, 8, 9]\n"
     ]
    }
   ],
   "source": [
    "def quick_sort_chu(a_list):\n",
    "    if len(a_list) < 2: return a_list\n",
    "    lesser = quick_sort([x for x in a_list[1:] if x <= a_list[0]])\n",
    "    bigger = quick_sort([x for x in a_list[1:] if x > a_list[0]])\n",
    "    return sum([lesser, [a_list[0]], bigger], [])\n",
    "A = [5,9,1,2,4,8,6,3,7]\n",
    "print(A)\n",
    "B = quick_sort_chu(A)\n",
    "print(B)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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