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39 lines
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39 lines
1.3 KiB
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<p>给你一个整数 <code>n</code>，请返回长度为 <code>n</code> 、仅由元音 (<code>a</code>, <code>e</code>, <code>i</code>, <code>o</code>, <code>u</code>) 组成且按 <strong>字典序排列</strong> 的字符串数量。</p>
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<p>字符串 <code>s</code> 按 <strong>字典序排列</strong> 需要满足：对于所有有效的 <code>i</code>，<code>s[i]</code> 在字母表中的位置总是与 <code>s[i+1]</code> 相同或在 <code>s[i+1]</code> 之前。</p>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre>
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<strong>输入：</strong>n = 1
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<strong>输出：</strong>5
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<strong>解释：</strong>仅由元音组成的 5 个字典序字符串为 <code>["a","e","i","o","u"]</code>
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</pre>
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<p><strong>示例 2：</strong></p>
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<pre>
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<strong>输入：</strong>n = 2
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<strong>输出：</strong>15
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<strong>解释：</strong>仅由元音组成的 15 个字典序字符串为
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["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"]
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注意，"ea" 不是符合题意的字符串，因为 'e' 在字母表中的位置比 'a' 靠后
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre>
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<strong>输入：</strong>n = 33
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<strong>输出：</strong>66045
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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 <= 50</code> </li>
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</ul>
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