Snakes and Ladders Python Solution with Tests

lcpy gen -n 909   # by problem number
lcpy gen -s snakes_and_ladders   # by problem name

Input: board = [[-1,-1,-1,-1,-1,-1],[-1,-1,-1,-1,-1,-1],[-1,-1,-1,-1,-1,-1],[-1,35,-1,-1,13,-1],[-1,-1,-1,-1,-1,-1],[-1,15,-1,-1,-1,-1]]
Output: 4
Explanation:
In the beginning, you start at square 1 = [5,0].
You decide to move to square 2 = [5,1], and must take the ladder at square 2 to go to square 15 = [3,0].
You decide to move to square 17 = [3,4], and must take the snake at square 17 to go to square 13 = [3,1].
You decide to move to square 18 = [3,5], and must take the board at square 18 to go to square 36 = [0,5].
You have 4 dice rolls to reach square 36, so return 4.

Input: board = [[-1,-1],[-1,3]]
Output: 1

from collections import deque


class Solution:
    # Time: O(n^2)
    # Space: O(n^2)
    def snakes_and_ladders(self, board: list[list[int]]) -> int:
        n = len(board)
        target = n * n

        def position(square: int) -> tuple[int, int]:
            row, col = divmod(square - 1, n)
            if row % 2 == 1:
                col = n - 1 - col
            return n - 1 - row, col

        moves = {1: 0}
        queue: deque[int] = deque([1])
        while queue:
            curr = queue.popleft()
            for nxt in range(curr + 1, min(curr + 6, target) + 1):
                row, col = position(nxt)
                dest = board[row][col] if board[row][col] != -1 else nxt
                if dest == target:
                    return moves[curr] + 1
                if dest not in moves:
                    moves[dest] = moves[curr] + 1
                    queue.append(dest)
        return -1