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46 lines
2.0 KiB
HTML
46 lines
2.0 KiB
HTML
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<p>Given a string <code>s</code>, determine if it is <strong>valid</strong>.</p>
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<p>A string <code>s</code> is <strong>valid</strong> if, starting with an empty string <code>t = ""</code>, you can <strong>transform </strong><code>t</code><strong> into </strong><code>s</code> after performing the following operation <strong>any number of times</strong>:</p>
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<ul>
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<li>Insert string <code>"abc"</code> into any position in <code>t</code>. More formally, <code>t</code> becomes <code>t<sub>left</sub> + "abc" + t<sub>right</sub></code>, where <code>t == t<sub>left</sub> + t<sub>right</sub></code>. Note that <code>t<sub>left</sub></code> and <code>t<sub>right</sub></code> may be <strong>empty</strong>.</li>
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</ul>
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<p>Return <code>true</code> <em>if </em><code>s</code><em> is a <strong>valid</strong> string, otherwise, return</em> <code>false</code>.</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 = "aabcbc"
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<strong>Output:</strong> true
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<strong>Explanation:</strong>
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"" -> "<u>abc</u>" -> "a<u>abc</u>bc"
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Thus, "aabcbc" is valid.</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "abcabcababcc"
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<strong>Output:</strong> true
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<strong>Explanation:</strong>
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"" -> "<u>abc</u>" -> "abc<u>abc</u>" -> "abcabc<u>abc</u>" -> "abcabcab<u>abc</u>c"
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Thus, "abcabcababcc" is valid.
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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 = "abccba"
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<strong>Output:</strong> false
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<strong>Explanation:</strong> It is impossible to get "abccba" using the operation.
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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 <= 2 * 10<sup>4</sup></code></li>
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<li><code>s</code> consists of letters <code>'a'</code>, <code>'b'</code>, and <code>'c'</code></li>
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</ul>
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