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50 lines
2.2 KiB
HTML
50 lines
2.2 KiB
HTML
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<p>You are given two strings <code>s</code> and <code>t</code> of equal length <code>n</code>. You can perform the following operation on the string <code>s</code>:</p>
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<ul>
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<li>Remove a <strong>suffix</strong> of <code>s</code> of length <code>l</code> where <code>0 < l < n</code> and append it at the start of <code>s</code>.<br />
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For example, let <code>s = 'abcd'</code> then in one operation you can remove the suffix <code>'cd'</code> and append it in front of <code>s</code> making <code>s = 'cdab'</code>.</li>
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</ul>
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<p>You are also given an integer <code>k</code>. Return <em>the number of ways in which </em><code>s</code> <em>can be transformed into </em><code>t</code><em> in <strong>exactly</strong> </em><code>k</code><em> operations.</em></p>
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<p>Since the answer can be large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "abcd", t = "cdab", k = 2
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<strong>Output:</strong> 2
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<strong>Explanation:</strong>
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First way:
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In first operation, choose suffix from index = 3, so resulting s = "dabc".
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In second operation, choose suffix from index = 3, so resulting s = "cdab".
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Second way:
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In first operation, choose suffix from index = 1, so resulting s = "bcda".
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In second operation, choose suffix from index = 1, so resulting s = "cdab".
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "ababab", t = "ababab", k = 1
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<strong>Output:</strong> 2
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<strong>Explanation:</strong>
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First way:
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Choose suffix from index = 2, so resulting s = "ababab".
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Second way:
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Choose suffix from index = 4, so resulting s = "ababab".
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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>2 <= s.length <= 5 * 10<sup>5</sup></code></li>
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<li><code>1 <= k <= 10<sup>15</sup></code></li>
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<li><code>s.length == t.length</code></li>
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<li><code>s</code> and <code>t</code> consist of only lowercase English alphabets.</li>
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</ul>
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