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35 lines
1.6 KiB
HTML
35 lines
1.6 KiB
HTML
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<p>Given a string s, return <em>the number of <strong>distinct non-empty subsequences</strong> of</em> <code>s</code>. Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
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A <strong>subsequence</strong> of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., <code>"ace"</code> is a subsequence of <code>"<u>a</u>b<u>c</u>d<u>e</u>"</code> while <code>"aec"</code> is not.
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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 = "abc"
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<strong>Output:</strong> 7
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<strong>Explanation:</strong> The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc".
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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 = "aba"
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<strong>Output:</strong> 6
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<strong>Explanation:</strong> The 6 distinct subsequences are "a", "b", "ab", "aa", "ba", and "aba".
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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 = "aaa"
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<strong>Output:</strong> 3
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<strong>Explanation:</strong> The 3 distinct subsequences are "a", "aa" and "aaa".
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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 <= 2000</code></li>
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<li><code>s</code> consists of lowercase English letters.</li>
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</ul>
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