test.py

a = [[1,2,1,1],
     [1,2,1,1],
     [1,2,1,1]]

STEPS = [
    lambda (x,y): (x+1,y),           # STEPS[0]
    lambda (x,y): (x,y+1),           # STEPS[1]
    lambda (x,y): (x-1,y),           # STEPS[2]
    lambda (x,y): (x,y-1),           # STEPS[3]
]

def next_step(cur,grid):
    cur_x, cur_y = cur
    which_change_step = grid[cur_y][cur_x] -1
    change_step = STEPS[which_change_step]
    return change_step(cur)

def in_grid(cur,grid):
    x,y = cur
    height = len(grid)
    if y >= height or y < 0:
        return False

    row = grid[y]
    width = len(row)
    if x >= len(row) or x < 0:
        return False

    return True

def labyrinth(start, end, grid):
    start_i, start_j = start
    end_i, end_j = end

    cur = start
    follow = start
    should_advance_follow = False
    while True:
        if cur == end:
            return True
        if cur is follow:
            return False
        if not in_grid(cur, grid):
            return False
        cur = next_step(cur, grid)

        if should_advance_follow:
            follow = next_step(follow, grid)
        shoould_advance_follow = not should_advance_follow