{
 "cells": [
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   "cell_type": "markdown",
   "source": [
    "Given an array of integers where 1 ≤ a[i] ≤ _n_ ( _n_ = size of array), some\n",
    "elements appear twice and others appear once.\n",
    "\n",
    "Find all the elements of [1, _n_ ] inclusive that do not appear in this array.\n",
    "\n",
    "Could you do it without extra space and in O( _n_ ) runtime? You may assume\n",
    "the returned list does not count as extra space.\n",
    "\n",
    "**Example:**\n",
    "\n",
    "\n",
    "\n",
    "    Input:\n",
    "    [4,3,2,7,8,2,3,1]\n",
    "\n",
    "    Output:\n",
    "    [5,6]"
   ],
   "metadata": {}
  },
  {
   "outputs": [
    {
     "output_type": "execute_result",
     "data": {
      "text/plain": "find_all_numbers_disappeared_in_an_array (generic function with 1 method)"
     },
     "metadata": {},
     "execution_count": 1
    }
   ],
   "cell_type": "code",
   "source": [
    "# @lc code=start\n",
    "using LeetCode\n",
    "\n",
    "function find_all_numbers_disappeared_in_an_array(arr::Vector{Int})\n",
    "    return setdiff(eachindex(arr), arr)\n",
    "end\n",
    "\n",
    "# add your code here:\n",
    "# @lc code=end"
   ],
   "metadata": {},
   "execution_count": 1
  },
  {
   "cell_type": "markdown",
   "source": [
    "---\n",
    "\n",
    "*This notebook was generated using [Literate.jl](https://github.com/fredrikekre/Literate.jl).*"
   ],
   "metadata": {}
  }
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