adventofcode2024/day18/sol.py

from collections import defaultdict
import astar

def parse(file):
    return [
        tuple([int(x) for x in line.strip().split(',')])
        for line in file
    ]

def solve(file, N=71, T=1024):
    falling = parse(file)
    inf = float('inf')
    map = defaultdict(lambda: 1)
    for i,p in enumerate(falling):
        if i > T:
            break
        map[p] = 0
    sol = _solve(map, N)
    print(sol)
    print(len(sol[-1])-1)

def _solve(map, N):
    start = (0,0) # x,y
    end = N-1, N-1
    
    def neighbors(n):
        x,y = n
        def push(x,y):
            if 0 <= x < N and 0 <= y < N:
                if map[x,y]:
                    out.append((1,(x,y)))
        out = []
        push(x+1,y)
        push(x,y+1)
        push(x-1,y)
        push(x,y-1)
        return out

    def heuristic(n):
        return abs(end[0] - n[0]) + abs(end[1] - n[1])

    return astar.search(start, end, neighbors, heuristic)

import math
def solve2(file, N):
    falling = parse(file)
    map = defaultdict(lambda: 1)
    for i,p in enumerate(falling):
        map[p] = 0
        sol = _solve(map, N)
        if math.isinf(sol[0]):
            print(p)
            break

solve(open("sample1.in"), N=7, T=12)
solve2(open("sample1.in"), N=7)
print()
solve(open("input"), N=71, T=1024)
solve2(open("input"), N=71)