Package g0001_0100.s0091_decode_ways

Class Solution

java.lang.Object

g0001_0100.s0091_decode_ways.Solution

public class Solution
extends Object

91 - Decode Ways.<p>Medium</p> <p>A message containing letters from <code>A-Z</code> can be <strong>encoded</strong> into numbers using the following mapping:</p> <p>&lsquo;A&rsquo; -> &ldquo;1&rdquo; &lsquo;B&rsquo; -> &ldquo;2&rdquo; &hellip; &lsquo;Z&rsquo; -> &ldquo;26&rdquo;</p> <p>To <strong>decode</strong> an encoded message, all the digits must be grouped then mapped back into letters using the reverse of the mapping above (there may be multiple ways). For example, <code>&quot;11106&quot;</code> can be mapped into:</p> <ul> <li><code>&quot;AAJF&quot;</code> with the grouping <code>(1 1 10 6)</code></li> <li><code>&quot;KJF&quot;</code> with the grouping <code>(11 10 6)</code></li> </ul> <p>Note that the grouping <code>(1 11 06)</code> is invalid because <code>&quot;06&quot;</code> cannot be mapped into <code>'F'</code> since <code>&quot;6&quot;</code> is different from <code>&quot;06&quot;</code>.</p> <p>Given a string <code>s</code> containing only digits, return <em>the <strong>number</strong> of ways to <strong>decode</strong> it</em>.</p> <p>The answer is guaranteed to fit in a <strong>32-bit</strong> integer.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> s = &ldquo;12&rdquo;</p> <p><strong>Output:</strong> 2</p> <p><strong>Explanation:</strong> &ldquo;12&rdquo; could be decoded as &ldquo;AB&rdquo; (1 2) or &ldquo;L&rdquo; (12).</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> s = &ldquo;226&rdquo;</p> <p><strong>Output:</strong> 3</p> <p><strong>Explanation:</strong> &ldquo;226&rdquo; could be decoded as &ldquo;BZ&rdquo; (2 26), &ldquo;VF&rdquo; (22 6), or &ldquo;BBF&rdquo; (2 2 6).</p> <p><strong>Example 3:</strong></p> <p><strong>Input:</strong> s = &ldquo;0&rdquo;</p> <p><strong>Output:</strong> 0</p> <p><strong>Explanation:</strong> There is no character that is mapped to a number starting with 0. The only valid mappings with 0 are &lsquo;J&rsquo; -> &ldquo;10&rdquo; and &lsquo;T&rsquo; -> &ldquo;20&rdquo;, neither of which start with 0. Hence, there are no valid ways to decode this since all digits need to be mapped.</p> <p><strong>Example 4:</strong></p> <p><strong>Input:</strong> s = &ldquo;06&rdquo;</p> <p><strong>Output:</strong> 0</p> <p><strong>Explanation:</strong> &ldquo;06&rdquo; cannot be mapped to &ldquo;F&rdquo; because of the leading zero (&ldquo;6&rdquo; is different from &ldquo;06&rdquo;).</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= s.length <= 100</code></li> <li><code>s</code> contains only digits and may contain leading zero(s).</li> </ul>

Constructor Summary

Constructors

Constructor	Description
Solution()

Method Summary

Modifier and Type	Method	Description
int	numDecodings(String s)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Solution

public Solution()

Method Details

numDecodings

public int numDecodings(String s)