diff --git a/2021/day15.py b/2021/day15.py new file mode 100644 index 0000000..a9add67 --- /dev/null +++ b/2021/day15.py @@ -0,0 +1,53 @@ +from collections import defaultdict +from math import inf + +with open("input15.txt") as f: + lines = [line.rstrip() for line in f] +plan = [list(map(int, line)) for line in lines] +dim = len(plan) +ndim = dim * 5 + + +# wanted to try something other than the yearly djikstra, so overkill and +# incomplete bellman-ford, precedents skipped for laughable gains. +def solve(dimension, risk_f): + dists = defaultdict(lambda: inf) + dists[(0, 0)] = 0 + changed = True + while changed: + changed = False + for x in range(dimension): + for y in range(dimension): + p = (x, y) + dist = dists[p] + near = [] + if x > 0: + near.append((x - 1, y)) + if x < dimension - 1: + near.append((x + 1, y)) + if y > 0: + near.append((x, y - 1)) + if y < dimension - 1: + near.append((x, y + 1)) + for n in near: + nx, ny = n + risk = risk_f(nx, ny) + if dist + risk < dists[n]: + changed = True + dists[n] = dist + risk + return dists + + +def risk_f1(nx, ny): + return plan[nx][ny] + + +def risk_f2(nx, ny): + risk = (plan[nx % dim][ny % dim] + nx // dim + ny // dim) + while risk >= 10: + risk -= 9 + return risk + + +print(solve(dim, risk_f1)[(dim - 1, dim - 1)]) +print(solve(ndim, risk_f2)[(ndim - 1, ndim - 1)])