Added README.md file for Snakes and Ladders

Author: ata-turhan

945-snakes-and-ladders/README.md

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+<h2><a href="https://leetcode.com/problems/snakes-and-ladders">Snakes and Ladders</a></h2> <img src='https://img.shields.io/badge/Difficulty-Medium-orange' alt='Difficulty: Medium' /><hr><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="_blank"><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> are not the starting points of any snake or ladder.</p>
+
+<p>Note that you only take a snake or ladder at most once per dice roll. If the destination to a snake or ladder is the start of another snake or ladder, you do <strong>not</strong> follow the subsequent&nbsp;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 dice rolls 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>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2018/09/23/snakes.png" style="width: 500px; height: 394px;" />
+<pre>
+<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]]
+<strong>Output:</strong> 4
+<strong>Explanation:</strong> 
+In the beginning, you start at square 1 (at row 5, column 0).
+You decide to move to square 2 and must take the ladder to square 15.
+You then decide to move to square 17 and must take the snake to square 13.
+You then decide to move to square 14 and must take the ladder to square 35.
+You then decide to move to square 36, ending the game.
+This is the lowest possible number of moves to reach the last square, so return 4.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> board = [[-1,-1],[-1,3]]
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>n == board.length == board[i].length</code></li>
+	<li><code>2 &lt;= n &lt;= 20</code></li>
+	<li><code>board[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> are not the starting points of any snake or ladder.</li>
+</ul>