My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add solution for 2023/24
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2023/day24.py
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2023/day24.py
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import fileinput
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from itertools import combinations
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from utils import parse_nums
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def find_intersection(x1, y1, x2, y2, x3, y3, x4, y4):
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# https://stackoverflow.com/a/51127674
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px = ((x1*y2-y1*x2)*(x3-x4)-(x1-x2)*(x3*y4-y3*x4)) / ((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4))
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py = ((x1*y2-y1*x2)*(y3-y4)-(y1-y2)*(x3*y4-y3*x4)) / ((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4))
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return [px, py]
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# Parse problem input.
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HAILSTONES = [tuple(parse_nums(line)) for line in fileinput.input()]
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MIN = 200000000000000
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MAX = 400000000000000
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part_1 = 0
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for a, b in combinations(HAILSTONES, 2):
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ax, ay, _, avx, avy, _ = a
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bx, by, _, bvx, bvy, _ = b
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a_slope = avy / avx
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a_b = ay - (a_slope * ax)
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a_start = a_slope * MIN + a_b
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a_end = a_slope * MAX + a_b
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b_slope = bvy / bvx
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b_b = by - (b_slope * bx)
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b_start = b_slope * MIN + b_b
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b_end = b_slope * MAX + b_b
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try:
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px, py = find_intersection(MIN, a_start, MAX, a_end, MIN, b_start, MAX, b_end)
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except:
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# Parallel lines.
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continue
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# Intersection in A's past
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if avx > 0 and px < ax:
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continue
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elif avx < 0 and px > ax:
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continue
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# Intersection in B's past
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if bvx > 0 and px < bx:
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continue
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elif bvx < 0 and px > bx:
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continue
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# Good intersection in zone.
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if MIN <= px <= MAX and MIN <= py <= MAX:
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part_1 += 1
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print("Part 1:", part_1)
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# Solve Part 2.
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try:
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from z3 import Real, Solver
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except:
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print("Part 2 requires z3 to be installed (`pip install z3-solver`)")
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import sys
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sys.exit()
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mx = Real('mx')
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my = Real('my')
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mz = Real('mz')
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mxv = Real('mxv')
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myv = Real('myv')
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mzv = Real('mzv')
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c = [Real('c' + str(n)) for n in range(len(HAILSTONES))]
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s = Solver()
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for i, (px, py, pz, vx, vy, vz) in enumerate(HAILSTONES):
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s.add(c[i] >= 0)
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s.add(mx + c[i] * mxv == px + c[i] * vx)
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s.add(my + c[i] * myv == py + c[i] * vy)
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s.add(mz + c[i] * mzv == pz + c[i] * vz)
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s.check()
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m = s.model()
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print("Part 2:", m[mx].as_long() + m[my].as_long() + m[mz].as_long())