aoc22/day12-2.py

import copy
from queue import PriorityQueue

MAX_PRIO = ord('z') - ord('a')
#log_this_is_n = 0
n_solutions = 0

q = PriorityQueue()


#def log_every_n(message):
#    global log_this_is_n

#    log_this_is_n = (log_this_is_n + 1) % 100000

#    if log_this_is_n == 0:
#        print(message)


class PossiblePath:
    def __init__(self, y, x, visited):
        self.x = x
        self.y = y
        self.visited = tuple(visited)

    def __lt__(self, other):
        return (len(self.visited) < len(other.visited) or
                self.x < other.x or
                self.y < other.y)


def MakeCandidate(x, y, visited, value_diff):
    if (y, x) in point_cost and point_cost[(y, x)] <= len(visited):
        return
    point_cost[(y, x)] = len(visited)

    prio_valuediff = value_diff * -1
    prio_distance = (max(End[0], x) - min(End[0], x)) + (max(End[1], y) - min(End[1], y))
    prio_lettervalue = MAX_PRIO - grid[y][x]
    prio_pathlen = (gridX * gridY) - len(visited)
    path = PossiblePath(y, x, visited)
    q.put((prio_valuediff, prio_distance, path))


def findPath():
    global fewestSteps
    global n_solutions
    while not q.empty():
        _, _, path = q.get()

        if (path.y, path.x) in point_cost and point_cost[(path.y, path.x)] < len(path.visited):
            # We already have a better path to the current point.
            continue

        #log_every_n('Inspecting: %dx%d, visited %d points, %d solutions' % (path.x, path.y, len(path.visited), n_solutions))
        visited = list(path.visited)
        if (path.y, path.x) in visited:
            continue
        visited.append((path.y, path.x))

        if (not (fewestSteps == None)) and (len(visited) - 1 >= fewestSteps):
            continue
        if [path.x, path.y] == End:
            n_solutions += 1
            print('Solution Found! Steps taken:', len(visited) - 1, 'Total Solutions', n_solutions)
            fewestSteps = len(visited) - 1
            
            continue

        if path.x > 0:
            if grid[path.y][path.x - 1] <= grid[path.y][path.x] + 1:
                valDiff = grid[path.y][path.x - 1] - grid[path.y][path.x]
                MakeCandidate(path.x - 1, path.y, visited, valDiff)
        if path.x < gridX:
            if grid[path.y][path.x + 1] <= grid[path.y][path.x] + 1:
                valDiff = grid[path.y][path.x + 1] - grid[path.y][path.x]
                MakeCandidate(path.x + 1, path.y, visited, valDiff)
        if path.y > 0:
            if grid[path.y - 1][path.x] <= grid[path.y][path.x] + 1:
                valDiff = grid[path.y - 1][path.x] - grid[path.y][path.x]
                MakeCandidate(path.x, path.y - 1, visited, valDiff)
        if path.y < gridY:
            if grid[path.y + 1][path.x] <= grid[path.y][path.x] + 1:
                valDiff = grid[path.y + 1][path.x] - grid[path.y][path.x]
                MakeCandidate(path.x, path.y + 1, visited, valDiff)


with open('input12.txt','r') as f:
    inp = f.read().splitlines(keepends=False)

grid = []
fewestSteps = None
Starts = []


for i in range(len(inp)):
    grid.append([])
    for j in range(len(inp[i])):
        if inp[i][j] == 'S':
            Starts.append([j, i])
            grid[i].append(0)
        elif inp[i][j] == 'E':
            End = [j, i]
            grid[i].append(ord('z') - ord('a'))
        else:
            if inp[i][j] == 'a':
                Starts.append([j, i])
            grid[i].append(ord(inp[i][j])-ord('a'))

gridX = len(grid[0]) - 1
gridY = len(grid) - 1
loopN = 0

print('possible starting locations found:', len(Starts))

for Start in Starts:
    loopN +=1
    print('Checking Location', loopN, 'out of', len(Starts))
    point_cost = {}
    _x = Start[0]
    _y = Start[1]
    if Start[0] > 0:
        if grid[_y][_x - 1] <= 1:
            MakeCandidate(_x - 1, _y, [(_y, _x)], grid[_y][_x - 1])
    if Start[0] < gridX:
        if grid[_y][_x + 1] <= 1:
            MakeCandidate(_x + 1, _y, [(_y, _x)], grid[_y][_x + 1])
    if Start[1] > 0:
        if grid[_y - 1][_x] <= 1:
            MakeCandidate(_x, _y - 1, [(_y, _x)], grid[_y - 1][_x])
    if Start[1] < gridY:
        if grid[_y + 1][_x] <= 1:
            MakeCandidate(_x, _y + 1, [(_y, _x)], grid[_y + 1][_x])

    findPath()

print('The shortest path takes', fewestSteps, 'steps')
#for x in grid:
#    tempa = ''
#    for y in x:
#        tempa += chr(y + 97)
#    print(tempa)