019-Solution.ipynb

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    "# You are given the following information, but you may prefer to do some research for yourself.\n",
    "\n",
    "### 1 Jan 1900 was a Monday.\n",
    "\n",
    "### Thirty days has September, April, June and November.\n",
    "\n",
    "### All the rest have thirty-one, saving February alone, which has twenty-eight, rain or shine.\n",
    "\n",
    "### And on leap years, twenty-nine.\n",
    "\n",
    "### A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.\n",
    "\n",
    "# How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?"
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    "_____\n",
    "\n",
    "### First, we'll find all the leap years"
   ]
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   "source": [
    "2000%400.0"
   ]
  },
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   "cell_type": "markdown",
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   "source": [
    "**$\\implies$ 2000 IS a leap year**"
   ]
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   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [],
   "source": [
    "list_leap_years = [x for x in range(1901, 2000) if x%4==0]+[2000]"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- Jan 1 1900 was on a Monday, so what was Jan 1 1901?"
   ]
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   "cell_type": "code",
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     "data": {
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       "1"
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     "execution_count": 42,
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   "source": [
    "365%7"
   ]
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   "source": [
    "**It was on a Tuesday**"
   ]
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   "source": [
    "______\n",
    "\n",
    "- Creating a list of the dates"
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   "execution_count": 41,
   "metadata": {},
   "outputs": [],
   "source": [
    "list_dates = []\n",
    "\n",
    "for year in range(1901,2001):\n",
    "    for month in range(1,13):\n",
    "        if month in [4,6,9,11]:\n",
    "            list_dates = list_dates+list(range(1,31))\n",
    "        elif month == 2:\n",
    "            if year in list_leap_years:\n",
    "                list_dates = list_dates+list(range(1,30))\n",
    "            else:\n",
    "                list_dates = list_dates+list(range(1,29))\n",
    "        else:\n",
    "            list_dates = list_dates+list(range(1,32))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- Since the list starts on a Tuesday, if we take every 6th element, we should get only the Sundays"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [],
   "source": [
    "list_sundays = list_dates[5::7]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- Now, we just need to take the elements of this list with a value of 1"
   ]
  },
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   "execution_count": 54,
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   "outputs": [
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     "data": {
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       "171"
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     "execution_count": 54,
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   "source": [
    "len([x for x in list_sundays if x==1])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Answer = 171"
   ]
  }
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