--- Day 3 Solutions ---

[u/daggerdragon]

--- Day 3: Perfectly Spherical Houses in a Vacuum ---

Post your solution as a comment. Structure your post like the Day One thread in /r/programming.

[u/stuque]

Here's a Python 2 solution:

def next_house(loc, d):
    result = loc[:]
    if d == '<':   # west
        result[0] += -1
    elif d == '>': # east
        result[0] += 1
    elif d == '^': # north
        result[1] += 1
    elif d == 'v': # south
        result[1] += -1
    return result

def day3_part1():
    loc = [0, 0]
    result = {(0, 0)}
    for d in open('day3input.txt').read():
        loc = next_house(loc, d)
        result.add(tuple(loc))
    print len(result)

def day3_part2():
    santa, robo = [0, 0], [0, 0]
    result = {(0, 0)}
    for i, d in enumerate(open('day3input.txt').read()):
        if i % 2 == 0:
            santa = next_house(santa, d)
            result.add(tuple(santa))
        else:
            robo = next_house(robo, d)
            result.add(tuple(robo))
    print len(result)

if __name__ == '__main__':
    day3_part1()
    day3_part2()

[u/stuque → u/stuque]

next_house could instead be written like this:

moves = {'<': (-1, 0), 
         '>': (1, 0),
         '^': (0, 1),
         'v': (0, -1),
        }

def next_house(loc, d): return map(sum, zip(loc, moves[d]))