euler/ipython/EulerProblem049.ipynb

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   "cell_type": "markdown",
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   "source": [
    "# Prime permutations (Euler Problem 49)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "[https://projecteuler.net/problem=49](https://projecteuler.net/problem=49)\n",
    "\n",
    "The arithmetic sequence, 1487, 4817, 8147, in which each of the terms increases by 3330, is unusual in two ways: (i) each of the three terms are prime, and, (ii) each of the 4-digit numbers are permutations of one another.\n",
    "\n",
    "There are no arithmetic sequences made up of three 1-, 2-, or 3-digit primes, exhibiting this property, but there is one other 4-digit increasing sequence.\n",
    "\n",
    "What 12-digit number do you form by concatenating the three terms in this sequence?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "def sieve_of_eratosthenes(number):\n",
    "    primes = []\n",
    "    prospects = [n for n in range(2, number)]\n",
    "    while prospects:\n",
    "        p = prospects[0]\n",
    "        prospects = [x for x in prospects if x % p != 0]\n",
    "        primes.append(p)\n",
    "        if p * p > number:\n",
    "            break\n",
    "    return primes + prospects\n",
    "\n",
    "ps = [p for p in sieve_of_eratosthenes(10000) if p > 1000]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [],
   "source": [
    "d = {}\n",
    "for p in ps:\n",
    "    s = \"\".join(sorted(str(p)))\n",
    "    try:\n",
    "        d[s].append(p)\n",
    "    except KeyError:\n",
    "        d[s] = [p]\n",
    "        \n",
    "pss = [value for key, value in d.items() if len(value) >= 3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[1487, 4817, 8147], [2969, 6299, 9629]]\n"
     ]
    }
   ],
   "source": [
    "def find_increasing_sequence(xs):\n",
    "    deltas = [(xs[j] - xs[i], i, j)\n",
    "        for i in range(0, len(xs) - 1)\n",
    "        for j in range(i + 1, len(xs))\n",
    "    ]\n",
    "    d = {}\n",
    "    for delta, i, j in deltas:\n",
    "        if delta in d and d[delta][-1] == i:\n",
    "            d[delta].append(j)\n",
    "        else:\n",
    "            d[delta] = [i, j]\n",
    "    for delta, sequence in d.items():\n",
    "        if len(sequence) == 3:\n",
    "            return [xs[index] for index in sequence]\n",
    "    return []\n",
    "\n",
    "s = [find_increasing_sequence(ps) for ps in pss if find_increasing_sequence(ps)]\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "296962999629\n"
     ]
    }
   ],
   "source": [
    "s = int(\"\".join(map(str, s[1])))\n",
    "assert(s == 296962999629)\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Congratulations, the answer you gave to problem 49 is correct.\n",
    "\n",
    "You are the 49654th person to have solved this problem.\n",
    "\n",
    "Nice work, failx, you've just advanced to Level 2 . \n",
    "46903 members (5.43%) have made it this far.\n",
    "\n",
    "This problem had a difficulty rating of 5%. The highest difficulty rating you have solved remains at 5%. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "completion_date": "Sun, 23 Dec 2018, 01:10",
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   "language": "python3.6",
   "name": "python3"
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   "version": "3.6.5"
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  "tags": [
   "permutations",
   "primes",
   "sequence"
  ]
 },
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