quick_sort.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "import random"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "nums = [7, 6, 5, 4, 3, 2, 1, 0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "def quick_select(left, right, k):\n",
    "    if left == right:\n",
    "        return\n",
    "    pivot_index = random.randint(left, right)\n",
    "    i, j = left, right\n",
    "    while True:\n",
    "        while nums[i] < nums[pivot_index]:\n",
    "            i += 1\n",
    "        while nums[j] > nums[pivot_index]:\n",
    "            j -= 1\n",
    "        if i >= j:\n",
    "            break\n",
    "        nums[i], nums[j] = nums[j], nums[i]\n",
    "\n",
    "    if left < i - 1:\n",
    "        quick_select(left, i - 1, k)\n",
    "    if right > i + 1:\n",
    "        quick_select(i + 1, right, k)\n",
    "    return nums[k-1]\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "quick_select(0, len(nums) - 1, 1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import defaultdict"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "nums = [1,1,1,2,2,3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "defaultdict(int, {1: 3, 2: 2, 3: 1})"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "counts = defaultdict(int)\n",
    "for num in nums:\n",
    "    counts[num] += 1\n",
    "counts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(1, 3), (2, 2), (3, 1)]"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "list(counts.items())"
   ]
  }
 ],
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