euler/ipython/EulerProblem052.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Permuted multiples (Euler Problem 52)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "[https://projecteuler.net/problem=52](https://projecteuler.net/problem=52)\n",
    "\n",
    "It can be seen that the number, 125874, and its double, 251748, contain exactly the same digits, but in a different order.\n",
    "\n",
    "Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {},
   "outputs": [],
   "source": [
    "from functools import reduce\n",
    "from operator import eq\n",
    "\n",
    "def get_length(n):\n",
    "    \"\"\" Returns the number of digits for n.\n",
    "        Returns wrong result for n = 0. \"\"\"\n",
    "    length = 0\n",
    "    while n:\n",
    "        length += 1\n",
    "        n //= 10\n",
    "    return length\n",
    "\n",
    "assert(get_length(100) == 3)\n",
    "\n",
    "def get_digits(n):\n",
    "    d = []\n",
    "    while n:\n",
    "        d.append(n % 10)\n",
    "        n //= 10\n",
    "    return d\n",
    "\n",
    "assert(get_digits(213) == [3, 1, 2])\n",
    "\n",
    "def get_digits_count(n):\n",
    "    digits_count = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]\n",
    "    for d in get_digits(n):\n",
    "        digits_count[d] += 1\n",
    "    return digits_count\n",
    "\n",
    "assert(get_digits_count(1258744) == [0, 1, 1, 0, 2, 1, 0, 1, 1, 0])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 64,
   "metadata": {},
   "outputs": [],
   "source": [
    "def check_if_multiples_contain_same_digits(n, max_multiple=2):\n",
    "    n_digits_count = get_digits_count(n)\n",
    "    n_length = get_length(n)\n",
    "    n_multiple = n * max_multiple\n",
    "    while n != n_multiple:\n",
    "        if n_length != get_length(n_multiple) or n_digits_count != get_digits_count(n_multiple):\n",
    "            return False\n",
    "        n_multiple -= n\n",
    "    return True\n",
    "\n",
    "assert(check_if_multiples_contain_same_digits(125874))\n",
    "assert(check_if_multiples_contain_same_digits(125875) == False)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 70,
   "metadata": {},
   "outputs": [],
   "source": [
    "for i in range(1, 10000000):\n",
    "    if check_if_multiples_contain_same_digits(i, 6):\n",
    "        s = i\n",
    "        break"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 72,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "142857\n"
     ]
    }
   ],
   "source": [
    "print(s)\n",
    "assert(s == 142857)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "completion_date": "Mon, 24 Dec 2018, 02:32",
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python3.6",
   "name": "python3"
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  "language_info": {
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    "name": "ipython",
    "version": 3
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   "file_extension": ".py",
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   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.6.5"
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  "tags": [
   "digits",
   "permutations"
  ]
 },
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