Package g0901_1000.s0909_snakes_and_ladders

Class Solution

java.lang.Object
g0901_1000.s0909_snakes_and_ladders.Solution
public class Solution extends Object
909 - Snakes and Ladders.<p>Medium</p> <p>You are given an <code>n x n</code> integer matrix <code>board</code> where the cells are labeled from <code>1</code> to <code>n<sup>2</sup></code> in a <a href="https://en.wikipedia.org/wiki/Boustrophedon" target="_top"><strong>Boustrophedon style</strong></a> starting from the bottom left of the board (i.e. <code>board[n - 1][0]</code>) and alternating direction each row.</p> <p>You start on square <code>1</code> of the board. In each move, starting from square <code>curr</code>, do the following:</p> <ul> <li>Choose a destination square <code>next</code> with a label in the range <code>[curr + 1, min(curr + 6, n<sup>2</sup>)]</code>. <ul> <li>This choice simulates the result of a standard <strong>6-sided die roll</strong>: i.e., there are always at most 6 destinations, regardless of the size of the board.</li> </ul> </li> <li>If <code>next</code> has a snake or ladder, you <strong>must</strong> move to the destination of that snake or ladder. Otherwise, you move to <code>next</code>.</li> <li>The game ends when you reach the square <code>n<sup>2</sup></code>.</li> </ul> <p>A board square on row <code>r</code> and column <code>c</code> has a snake or ladder if <code>board[r][c] != -1</code>. The destination of that snake or ladder is <code>board[r][c]</code>. Squares <code>1</code> and <code>n<sup>2</sup></code> do not have a snake or ladder.</p> <p>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 <strong>not</strong> follow the subsequent snake or ladder.</p> <ul> <li>For example, suppose the board is <code>[[-1,4],[-1,3]]</code>, and on the first move, your destination square is <code>2</code>. You follow the ladder to square <code>3</code>, but do <strong>not</strong> follow the subsequent ladder to <code>4</code>.</li> </ul> <p>Return <em>the least number of moves required to reach the square</em> <code>n<sup>2</sup></code><em>. If it is not possible to reach the square, return</em> <code>-1</code>.</p> <p><strong>Example 1:</strong></p> <p><img src="https://assets.leetcode.com/uploads/2018/09/23/snakes.png" alt="" /></p> <p><strong>Input:</strong> 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]]</p> <p><strong>Output:</strong> 4</p> <p><strong>Explanation:</strong></p> <p>In the beginning, you start at square 1 (at row 5, column 0).</p> <p>You decide to move to square 2 and must take the ladder to square 15.</p> <p>You then decide to move to square 17 and must take the snake to square 13.</p> <p>You then decide to move to square 14 and must take the ladder to square 35.</p> <p>You then decide to move to square 36, ending the game.</p> <p>This is the lowest possible number of moves to reach the last square, so return 4.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> board = [[-1,-1],[-1,3]]</p> <p><strong>Output:</strong> 1</p> <p><strong>Constraints:</strong></p> <ul> <li><code>n == board.length == board[i].length</code></li> <li><code>2 <= n <= 20</code></li> <li><code>grid[i][j]</code> is either <code>-1</code> or in the range <code>[1, n<sup>2</sup>]</code>.</li> <li>The squares labeled <code>1</code> and <code>n<sup>2</sup></code> do not have any ladders or snakes.</li> </ul>

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • snakesAndLadders

      public int snakesAndLadders(int[][] board)