Advent of Code 2022 - 9

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Day 9: Rope Bridge

https://adventofcode.com/2022/day/9

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with open('09.txt', 'r') as fp:
    lines = fp.readlines()
motions = [line.strip().split() for line in lines]

move = {
    'U': [0, 1],
    'D': [0, -1],
    'L': [-1, 0],
    'R': [1, 0],
}

Part One

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visited = set()
hx, hy = 0, 0
tx, ty = 0, 0
for m in motions:
    dir, step = m
    step = int(step)
    for i in range(step):
        hx = hx + move[dir][0]
        hy = hy + move[dir][1]
        dx = hx - tx
        dy = hy - ty
        if abs(dx) >= 2 or abs(dy) >= 2:
            tx += int(dx>0) - int(dx<0)
            ty += int(dy>0) - int(dy<0)
        visited.add((tx, ty))
print(len(visited))

Answer: 6332

Part Two

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visited = set()
hx, hy = 0, 0
tx, ty = 0, 0
rope = [(0, 0)] * 10
for m in motions:
    dir, step = m
    step = int(step)
    for i in range(step):
        hx, hy = rope[0]
        hx = hx + move[dir][0]
        hy = hy + move[dir][1]
        rope[0] = (hx, hy)
        for j in range(len(rope)-1):
            hx, hy = rope[j]
            tx, ty = rope[j+1]
            dx = hx - tx
            dy = hy - ty
            if abs(dx) >= 2 or abs(dy) >= 2:
                tx += int(dx>0) - int(dx<0)
                ty += int(dy>0) - int(dy<0)
                rope[j+1] = (tx, ty)
            visited.add(rope[-1])
print(len(visited))

Answer: 2511