day09.py

#! /usr/bin/python3
import sys

dir = {"R": (1, 0), "U": (0, 1), "L": (-1, 0), "D": (0, -1)}


def mul(a, v):
    return (v[0] * a, v[1] * a)


def add(v1, v2):
    x, y = v1
    a, b = v2
    return (x + a, y + b)


def diff(v1, v2):
    x, y = v1
    a, b = v2
    return (x - a, y - b)


def distance(v1, v2):
    x, y = v1
    a, b = v2
    return (a - x)**2 + (b - y)**2


physics = {
    (2, 0): (1, 0),
    (2, 1): (1, 1),
    (1, 2): (1, 1),
    (0, 2): (0, 1),
    (-1, 2): (-1, 1),
    (-2, 1): (-1, 1),
    (-2, 0): (-1, 0),
    (-2, -1): (-1, -1),
    (-1, -2): (-1, -1),
    (0, -2): (0, -1),
    (1, -2): (1, -1),
    (2, -1): (1, -1),
    (-2, -2): (-1, -1),
    (-2, 2): (-1, 1),
    (2, -2): (1, -1),
    (2, 2): (1, 1),
}

position = [(0, 0) for _ in range(10)]
tails = set([(0, 0)])
for l in sys.stdin.readlines():
    cmd, num = [l.strip().split(' ')[0], int(l.strip().split(' ')[1])]

    for _ in range(0, num):
        position[0] = add(position[0], dir[cmd])
        for i in range(1, 10):
            new_head, tail = position[i-1:i+1]
            new_tail = tail
            if distance(new_head, tail) > 2:
                d = physics[diff(new_head, tail)]
                new_tail = add(tail, d)

            position[i] = new_tail
        tails.add(position[-1])

print(len(tails))