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59 lines
2.4 KiB
HTML
59 lines
2.4 KiB
HTML
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<p>一个 「开心字符串」定义为：</p>
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<ul>
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<li>仅包含小写字母 <code>['a', 'b', 'c']</code>.</li>
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<li>对所有在 <code>1</code> 到 <code>s.length - 1</code> 之间的 <code>i</code> ，满足 <code>s[i] != s[i + 1]</code> （字符串的下标从 1 开始）。</li>
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</ul>
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<p>比方说，字符串 <strong>"abc"</strong>，<strong>"ac"，"b"</strong> 和 <strong>"abcbabcbcb"</strong> 都是开心字符串，但是 <strong>"aa"</strong>，<strong>"baa"</strong> 和 <strong>"ababbc"</strong> 都不是开心字符串。</p>
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<p>给你两个整数 <code>n</code> 和 <code>k</code> ，你需要将长度为 <code>n</code> 的所有开心字符串按字典序排序。</p>
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<p>请你返回排序后的第 k 个开心字符串，如果长度为 <code>n</code> 的开心字符串少于 <code>k</code> 个，那么请你返回 <strong>空字符串</strong> 。</p>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre><strong>输入：</strong>n = 1, k = 3
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<strong>输出：</strong>"c"
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<strong>解释：</strong>列表 ["a", "b", "c"] 包含了所有长度为 1 的开心字符串。按照字典序排序后第三个字符串为 "c" 。
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</pre>
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<p><strong>示例 2：</strong></p>
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<pre><strong>输入：</strong>n = 1, k = 4
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<strong>输出：</strong>""
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<strong>解释：</strong>长度为 1 的开心字符串只有 3 个。
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre><strong>输入：</strong>n = 3, k = 9
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<strong>输出：</strong>"cab"
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<strong>解释：</strong>长度为 3 的开心字符串总共有 12 个 ["aba", "abc", "aca", "acb", "bab", "bac", "bca", "bcb", "cab", "cac", "cba", "cbc"] 。第 9 个字符串为 "cab"
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</pre>
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<p><strong>示例 4：</strong></p>
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<pre><strong>输入：</strong>n = 2, k = 7
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<strong>输出：</strong>""
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</pre>
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<p><strong>示例 5：</strong></p>
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<pre><strong>输入：</strong>n = 10, k = 100
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<strong>输出：</strong>"abacbabacb"
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</pre>
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<p> </p>
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<p><strong>提示：</strong></p>
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<ul>
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<li><code>1 <= n <= 10</code></li>
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<li><code>1 <= k <= 100</code></li>
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</ul>
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<p> </p>
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