{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [],
   "source": [
    "instructions = [l.strip() for l in open('../../data/01-mowmaster.txt')]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Part 1\n",
    "`startswith()` isn't useful that often, but it makes for easily readable code when it is."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1136"
      ]
     },
     "execution_count": 31,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "non_comments = 0\n",
    "for i in instructions:\n",
    "    if not i.startswith('#'):\n",
    "        non_comments += 1\n",
    "non_comments"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This sort if simple walking along a list is sometimes easier with a list comprehension. \n",
    "\n",
    "In this case, I transform each element into the number 1, but only if it's not a comment. Then I sum all the 1s, which is the number of non-comment lines."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1136"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sum(1 for i in instructions if not i.startswith('#'))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Or, as a one-liner:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1136"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sum(1 for i in open('../../data/01-mowmaster.txt') if not i.startswith('#'))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "How many comments and total lines?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "395"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sum(1 for i in instructions if i.startswith('#'))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1531"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "len(instructions)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Part 2\n",
    "\n",
    "I have the `mower` as an \"object\" storing its state. (In this case, the mower is a `dict` and the state is just its location and direction.) As each instruction is executed, the mower is updated."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "An initial mower. I adopt the Scratch convention that a heading of 0 degrees is up, increasing clockwise; so right is 90 degrees."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [],
   "source": [
    "def init_mowmaster():\n",
    "    return {'x': 0, 'y': 0, 'd': 90}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Execute the instructions. Do them one at a time, updating the mowmaster for each one.\n",
    "\n",
    "(Can you see an accumulator pattern again?)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [],
   "source": [
    "def execute(mowmaster, instructions, debug=False):\n",
    "    for instruction in instructions:\n",
    "        mowmaster = execute_one(mowmaster, instruction, debug=debug)\n",
    "    return mowmaster"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Execute one instruction. If it starts `C` or `A`, turn; if it starts `F`, move forward. Ignore all other instructions."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "def execute_one(mowmaster, instruction, debug=False):\n",
    "    if instruction == 'C':\n",
    "        mowmaster['d'] = (mowmaster['d'] + 90) % 360 # Use the modulus operator to keep the angle in the range 0--360\n",
    "    elif instruction == 'A':\n",
    "        mowmaster['d'] = (mowmaster['d'] - 90) % 360\n",
    "    elif instruction.startswith('F'):\n",
    "        mowmaster = move(mowmaster, int(instruction[1:]))\n",
    "    if debug: \n",
    "        print(instruction, mowmaster)\n",
    "    return mowmaster"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The movement. Update `x` or `y` depending on the direction."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [],
   "source": [
    "def move(mower, distance):\n",
    "    if mower['d'] == 0:\n",
    "        mower['y'] += distance\n",
    "    elif mower['d'] == 90:\n",
    "        mower['x'] += distance\n",
    "    elif mower['d'] == 180:\n",
    "        mower['y'] -= distance\n",
    "    elif mower['d'] == 270:\n",
    "        mower['x'] -= distance\n",
    "    else:\n",
    "        raise ValueError\n",
    "    return mower"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Finally, how far the Mowmaster has moved."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [],
   "source": [
    "def mowmaster_distance(mw):\n",
    "    return abs(mw['x']) + abs(mw['y'])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now we have all the parts, put them together into the solution."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "337"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "mw = init_mowmaster()\n",
    "execute(mw, instructions)\n",
    "mowmaster_distance(mw)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.6.5"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}