{ "data": { "question": { "questionId": "945", "questionFrontendId": "909", "categoryTitle": "Algorithms", "boundTopicId": 1386, "title": "Snakes and Ladders", "titleSlug": "snakes-and-ladders", "content": "
You are given an n x n
integer matrix board
where the cells are labeled from 1
to n2
in a Boustrophedon style starting from the bottom left of the board (i.e. board[n - 1][0]
) and alternating direction each row.
You start on square 1
of the board. In each move, starting from square curr
, do the following:
next
with a label in the range [curr + 1, min(curr + 6, n2)]
.\n\n\tnext
has a snake or ladder, you must move to the destination of that snake or ladder. Otherwise, you move to next
.n2
.A board square on row r
and column c
has a snake or ladder if board[r][c] != -1
. The destination of that snake or ladder is board[r][c]
. Squares 1
and n2
do not have a snake or ladder.
Note that you only take a snake or ladder at most once per move. If the destination to a snake or ladder is the start of another snake or ladder, you do not follow the subsequent snake or ladder.
\n\n[[-1,4],[-1,3]]
, and on the first move, your destination square is 2
. You follow the ladder to square 3
, but do not follow the subsequent ladder to 4
.Return the least number of moves required to reach the square n2
. If it is not possible to reach the square, return -1
.
\n
Example 1:
\n\n\nInput: 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]]\nOutput: 4\nExplanation: \nIn the beginning, you start at square 1 (at row 5, column 0).\nYou decide to move to square 2 and must take the ladder to square 15.\nYou then decide to move to square 17 and must take the snake to square 13.\nYou then decide to move to square 14 and must take the ladder to square 35.\nYou then decide to move to square 36, ending the game.\nThis is the lowest possible number of moves to reach the last square, so return 4.\n\n\n
Example 2:
\n\n\nInput: board = [[-1,-1],[-1,3]]\nOutput: 1\n\n\n
\n
Constraints:
\n\nn == board.length == board[i].length
2 <= n <= 20
board[i][j]
is either -1
or in the range [1, n2]
.1
and n2
do not have any ladders or snakes.给你一个大小为 n x n
的整数矩阵 board
,方格按从 1
到 n2
编号,编号遵循 转行交替方式 ,从左下角开始 (即,从 board[n - 1][0]
开始)每一行交替方向。
玩家从棋盘上的方格 1
(总是在最后一行、第一列)开始出发。
每一回合,玩家需要从当前方格 curr
开始出发,按下述要求前进:
next
,目标方格的编号符合范围 [curr + 1, min(curr + 6, n2)]
。\n\n\tnext
处存在蛇或梯子,那么玩家会传送到蛇或梯子的目的地。否则,玩家传送到目标方格 next
。 n2
的方格时,游戏结束。r
行 c
列的棋盘,按前述方法编号,棋盘格中可能存在 “蛇” 或 “梯子”;如果 board[r][c] != -1
,那个蛇或梯子的目的地将会是 board[r][c]
。编号为 1
和 n2
的方格上没有蛇或梯子。
注意,玩家在每回合的前进过程中最多只能爬过蛇或梯子一次:就算目的地是另一条蛇或梯子的起点,玩家也 不能 继续移动。
\n\n[[-1,4],[-1,3]]
,第一次移动,玩家的目标方格是 2
。那么这个玩家将会顺着梯子到达方格 3
,但 不能 顺着方格 3
上的梯子前往方格 4
。返回达到编号为 n2
的方格所需的最少移动次数,如果不可能,则返回 -1
。
\n\n
示例 1:
\n\n\n输入: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]]\n输出:4\n解释:\n首先,从方格 1 [第 5 行,第 0 列] 开始。 \n先决定移动到方格 2 ,并必须爬过梯子移动到到方格 15 。\n然后决定移动到方格 17 [第 3 行,第 4 列],必须爬过蛇到方格 13 。\n接着决定移动到方格 14 ,且必须通过梯子移动到方格 35 。 \n最后决定移动到方格 36 , 游戏结束。 \n可以证明需要至少 4 次移动才能到达最后一个方格,所以答案是 4 。 \n\n\n
示例 2:
\n\n\n输入:board = [[-1,-1],[-1,3]]\n输出:1\n\n\n
\n\n
提示:
\n\nn == board.length == board[i].length
2 <= n <= 20
grid[i][j]
的值是 -1
或在范围 [1, n2]
内1
和 n2
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