adventofcode2021/aoc5-2.py

class FloorMap:
    def __init__(self, size_x, size_y):
        self.board = []
        for _ in range(size_y+1):
            self.board.append([0]*(size_x+1))

    def add_line(self, start_pos, end_pos):
        if start_pos[0] == end_pos[0]: # Vertical line: X stays constant, Y changes
            if start_pos[1] > end_pos[1]:
                start_pos, end_pos = end_pos, start_pos
            for i in range(start_pos[1], end_pos[1]+1):
                self.board[i][start_pos[0]] = self.board[i][start_pos[0]] + 1
        elif start_pos[1] == end_pos[1]: # Horizontal line: Y stays constant, X changes
            if start_pos[0] > end_pos[0]:
                start_pos, end_pos = end_pos, start_pos
            for i in range(start_pos[0], end_pos[0]+1):
                self.board[start_pos[1]][i] = self.board[start_pos[1]][i] + 1
        else: # Diagonal line: X and Y both change
            # These are only ever 45° angles, so each changes by 1 per iteration.
            if start_pos[0] > end_pos[0]:
                start_pos, end_pos = end_pos, start_pos
            i, j = start_pos
            end_i, end_j = end_pos[0], end_pos[1]
            # I've arranged this so X always increases. Y can either increase or decrease.
            # I don't like that so much repeats.
            # What I WANT to do here is be able to set a toggle variable so that
            # if Y decreases, the second condition flips from <= to >=,
            # and then j += dir, which is either 1 or -1.
            # But I can't find a way to do it without eval() bullshit.
            if j <= end_j: # there should be no cases where they're equal, but...
                while i <= end_i and j <= end_j:
                    self.board[j][i] = self.board[j][i] + 1
                    i += 1
                    j += 1
            else:
                while i <= end_i and j >= end_j:
                    self.board[j][i] = self.board[j][i] + 1                    
                    i += 1
                    j -= 1

    def count_inters(self):
        return sum([len([el for el in line if el >= 2]) for line in self.board])

    def __repr__(self):
        outstr = ""
        for line_num in range(10):
            outstr += f"{' '.join(str(self.board[line_num]))}"
        return outstr

    def __str__(self):
        outstr = ""
        for line_num in range(10):
            outstr += f"{' '.join(str(self.board[line_num]))}"
        return outstr


def main():
    with open("aoc5-1.txt", "r") as file:
        lines = [line.strip() for line in file.readlines()]
    # Each line is a pair of x,y coordinates...es separated by " -> " 
    lines = [[list(map(int, el.split(","))) for el in line.split(" -> ")] for line in lines]
    # god, this feels goofy, but it works
    size_x = max([max(line[0][0], line[1][0]) for line in lines])
    size_y = max([max(line[0][1], line[1][1]) for line in lines])
    board_map = FloorMap(size_x, size_y)
    for line in lines:
        board_map.add_line(*line)
    print(board_map.count_inters())


if __name__ == "__main__":
    main()