Project Euler Q14 - LO Man Hei

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    "### Q14\n",
    "Which starting number, under one million, produces the longest chain?"
   ]
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    "def collatz_walker(num, collatz_map):\n",
    "    if num in collatz_map:\n",
    "        return collatz_map[num]\n",
    "    elif num == 1:\n",
    "        collatz_map[1] = 0\n",
    "        return\n",
    "    collatz_map[num] = collatz_walker(3*num+1 if num % 2 else num//2, collatz_map)+1\n",
    "    return collatz_map[num]\n",
    "            \n",
    "def get_collatz_map(max_value, exclude_end = True):\n",
    "    collatz_map = {}\n",
    "    if not exclude_end:\n",
    "        max_value += 1\n",
    "    for i in range(1,max_value):\n",
    "        collatz_walker(i,collatz_map)\n",
    "    return collatz_map\n",
    "\n",
    "def max_value_key(data_dict):    \n",
    "    return sorted(data_dict.items(),key= lambda x : x[1],reverse=True)[0][0]"
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      "CPU times: user 1.34 s, sys: 68.9 ms, total: 1.41 s\n",
      "Wall time: 1.41 s\n"
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       "837799"
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   "source": [
    "%%time\n",
    "max_value_key(get_collatz_map(1000000))"
   ]
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