December 16th

The puzzle of day 16 was a lot of instructions for a fairly trivial coding problem.

My pitfall for this puzzle: The code is very inelegant, lots of if statements, and unfortunately no time to refactor this one.

Solution here, do not click if you want to solve the puzzle first yourself

#!/usr/bin/env python3

with open('input-small.txt') as infile:
    lines = infile.readlines()

grid = []
for line in lines:
    grid.append([c for c in line.strip()])

def trace(beam, grid, visited):
    x = beam[1]
    y = beam[0]
    direction = beam[2]
    while True:
        if y < 0 or y >= len(grid) or x < 0 or x >= len(grid[0]):
            return []
        tile = grid[y][x]
        if (y, x, direction) in visited:
            return []
        else: 
            visited.append((y, x, direction))
        if tile == '|':
            if direction == 'left' or direction == 'right':
                return [(y - 1, x, 'up'), (y + 1, x, 'down')] 
        elif tile == '-':
            if direction == 'up' or direction == 'down':
                return [(y, x - 1, 'left'), (y, x + 1, 'right')]
        elif tile == '\\':
            if direction == 'up':
                return [(y, x - 1, 'left')]
            elif direction == 'down':
                return [(y, x + 1, 'right')]
            if direction == 'right':
                return [(y + 1, x, 'down')]
            elif direction == 'left':
                return [(y - 1, x, 'up')]
        elif tile == '/':
            if direction == 'up':
                return [(y, x + 1, 'right')]
            elif direction == 'down':
                return [(y, x - 1, 'left')]
            if direction == 'right':
                return [(y - 1, x, 'up')]
            elif direction == 'left':
                return [(y + 1, x, 'down')]
        if direction == 'right':
            x += 1
        elif direction == 'left':
            x -= 1
        elif direction == 'up':
            y -= 1
        elif direction == 'down':
            y += 1

def calc_energized(start, grid):
    beams = [start]
    visited = []
    while beams:
        beams.extend(trace(beams.pop(), grid, visited))
    visited = set([(v[0], v[1]) for v in visited])
    result = len(visited)
    print(f'{start} = {result}')
    return result

start_coords = []
start_coords.extend([(0, x, 'down') for x in range(len(grid[0]))])
start_coords.extend([(y, len(grid[0]) - 1, 'left') for y in range(len(grid))])
start_coords.extend([(len(grid) - 1, x, 'up') for x in range(len(grid[0]))])
start_coords.extend([(y, 0, 'right') for y in range(len(grid))])

print(max([calc_energized(s, grid) for s in start_coords]))

That's it! See you again tomorrow!

Advent of Code 2023 - December 16th

December 16th