aoc-2019-c

Advent of Code 2019 Solutions in C
git clone https://git.sinitax.com/sinitax/aoc-2019-c
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part1 (3255B)

      1--- Day 15: Oxygen System ---
      2
      3Out here in deep space, many things can go wrong. Fortunately, many of those things have indicator
      4lights. Unfortunately, one of those lights is lit: the oxygen system for part of the ship has
      5failed!
      6
      7According to the readouts, the oxygen system must have failed days ago after a rupture in oxygen
      8tank two; that section of the ship was automatically sealed once oxygen levels went dangerously low.
      9A single remotely-operated repair droid is your only option for fixing the oxygen system.
     10
     11The Elves' care package included an Intcode program (your puzzle input) that you can use to remotely
     12control the repair droid. By running that program, you can direct the repair droid to the oxygen
     13system and fix the problem.
     14
     15The remote control program executes the following steps in a loop forever:
     16
     17
     18 - Accept a movement command via an input instruction.
     19
     20 - Send the movement command to the repair droid.
     21
     22 - Wait for the repair droid to finish the movement operation.
     23
     24 - Report on the status of the repair droid via an output instruction.
     25
     26
     27Only four movement commands are understood: north (1), south (2), west (3), and east (4). Any other
     28command is invalid. The movements differ in direction, but not in distance: in a long enough
     29east-west hallway, a series of commands like 4,4,4,4,3,3,3,3 would leave the repair droid back where
     30it started.
     31
     32The repair droid can reply with any of the following status codes:
     33
     34
     35 - 0: The repair droid hit a wall. Its position has not changed.
     36
     37 - 1: The repair droid has moved one step in the requested direction.
     38
     39 - 2: The repair droid has moved one step in the requested direction; its new position is the
     40location of the oxygen system.
     41
     42
     43You don't know anything about the area around the repair droid, but you can figure it out by
     44watching the status codes.
     45
     46For example, we can draw the area using D for the droid, # for walls, . for locations the droid can
     47traverse, and empty space for unexplored locations.  Then, the initial state looks like this:
     48
     49      
     50      
     51   D  
     52      
     53      
     54
     55To make the droid go north, send it 1. If it replies with 0, you know that location is a wall and
     56that the droid didn't move:
     57
     58      
     59   #  
     60   D  
     61      
     62      
     63
     64To move east, send 4; a reply of 1 means the movement was successful:
     65
     66      
     67   #  
     68   .D 
     69      
     70      
     71
     72Then, perhaps attempts to move north (1), south (2), and east (4) are all met with replies of 0:
     73
     74      
     75   ## 
     76   .D#
     77    # 
     78      
     79
     80Now, you know the repair droid is in a dead end. Backtrack with 3 (which you already know will get a
     81reply of 1 because you already know that location is open):
     82
     83      
     84   ## 
     85   D.#
     86    # 
     87      
     88
     89Then, perhaps west (3) gets a reply of 0, south (2) gets a reply of 1, south again (2) gets a reply
     90of 0, and then west (3) gets a reply of 2:
     91
     92      
     93   ## 
     94  #..#
     95  D.# 
     96   #  
     97
     98Now, because of the reply of 2, you know you've found the oxygen system! In this example, it was
     99only 2 moves away from the repair droid's starting position.
    100
    101What is the fewest number of movement commands required to move the repair droid from its starting
    102position to the location of the oxygen system?
    103
    104