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55 lines
2.1 KiB
HTML
55 lines
2.1 KiB
HTML
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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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<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>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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<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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</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>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><strong>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).
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "226"
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<strong>Output:</strong> 3
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<strong>Explanation:</strong> "226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).
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</pre>
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<p><strong>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").
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= s.length <= 100</code></li>
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<li><code>s</code> contains only digits and may contain leading zero(s).</li>
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</ul>
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