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Copy file name to clipboardExpand all lines: solution/0000-0099/0091.Decode Ways/README_EN.md
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<!-- description:start -->
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<p>A message containing letters from <code>A-Z</code> can be <strong>encoded</strong> into numbers using the following mapping:</p>
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<p>You have intercepted a secret message encoded as a string of numbers. The message is <strong>decoded</strong> via the following mapping:</p>
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<pre>
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'A' ->"1"
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'B' ->"2"
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...
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'Z' ->"26"
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</pre>
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<p><code>"1" ->'A'<br />
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"2" ->'B'<br />
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...<br />
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"25" ->'Y'<br />
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"26" ->'Z'</code></p>
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<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>"11106"</code> can be mapped into:</p>
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<p>However, while decoding the message, you realize that there are many different ways you can decode the message because some codes are contained in other codes (<code>"2"</code> and <code>"5"</code> vs <code>"25"</code>).</p>
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<p>For example, <code>"11106"</code> can be decoded into:</p>
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<ul>
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<li><code>"AAJF"</code> with the grouping <code>(1 1 10 6)</code></li>
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<li><code>"KJF"</code> with the grouping <code>(11 10 6)</code></li>
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<li><code>"AAJF"</code> with the grouping <code>(1, 1, 10, 6)</code></li>
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<li><code>"KJF"</code> with the grouping <code>(11, 10, 6)</code></li>
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<li>The grouping <code>(1, 11, 06)</code> is invalid because <code>"06"</code> is not a valid code (only <code>"6"</code> is valid).</li>
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</ul>
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<p>Note that the grouping <code>(1 11 06)</code> is invalid because <code>"06"</code> cannot be mapped into <code>'F'</code> since <code>"6"</code> is different from <code>"06"</code>.</p>
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<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>
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<p>Note: there may be strings that are impossible to decode.<br />
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<br />
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Given a string s containing only digits, return the <strong>number of ways</strong> to <strong>decode</strong> it. If the entire string cannot be decoded in any valid way, return <code>0</code>.</p>
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<p>The test cases are generated so that the answer fits in a <strong>32-bit</strong> integer.</p>
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<p> </p>
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<p><strongclass="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "12"
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> "12" could be decoded as "AB" (1 2) or "L" (12).
<p>"226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).</p>
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</div>
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<p><strongclass="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> s = "06"
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> "06" cannot be mapped to "F" because of the leading zero ("6" is different from "06").
<p>"06" cannot be mapped to "F" because of the leading zero ("6" is different from "06"). In this case, the string is not a valid encoding, so return 0.</p>
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