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40 lines
1.8 KiB
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40 lines
1.8 KiB
HTML
<p>Given two strings <code>s</code> and <code>t</code>, return <em>the number of distinct subsequences of <code>s</code> which equals <code>t</code></em>.</p>
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<p>A string's <strong>subsequence</strong> is a new string formed from the original string by deleting some (can be none) of the characters without disturbing the remaining characters' relative positions. (i.e., <code>"ACE"</code> is a subsequence of <code>"ABCDE"</code> while <code>"AEC"</code> is not).</p>
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<p>The test cases are generated so that the answer fits on a 32-bit signed 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 = "rabbbit", t = "rabbit"
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<strong>Output:</strong> 3
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<strong>Explanation:</strong>
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As shown below, there are 3 ways you can generate "rabbit" from S.
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<code><strong><u>rabb</u></strong>b<strong><u>it</u></strong></code>
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<code><strong><u>ra</u></strong>b<strong><u>bbit</u></strong></code>
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<code><strong><u>rab</u></strong>b<strong><u>bit</u></strong></code>
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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 = "babgbag", t = "bag"
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<strong>Output:</strong> 5
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<strong>Explanation:</strong>
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As shown below, there are 5 ways you can generate "bag" from S.
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<code><strong><u>ba</u></strong>b<u><strong>g</strong></u>bag</code>
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<code><strong><u>ba</u></strong>bgba<strong><u>g</u></strong></code>
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<code><u><strong>b</strong></u>abgb<strong><u>ag</u></strong></code>
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<code>ba<u><strong>b</strong></u>gb<u><strong>ag</strong></u></code>
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<code>babg<strong><u>bag</u></strong></code></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, t.length <= 1000</code></li>
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<li><code>s</code> and <code>t</code> consist of English letters.</li>
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</ul>
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