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31 lines
740 B
HTML
31 lines
740 B
HTML
<p>Given an integer <code>num</code>, repeatedly add all its digits until the result has only one digit, and return it.</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> num = 38
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The process is
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38 --> 3 + 8 --> 11
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11 --> 1 + 1 --> 2
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Since 2 has only one digit, return it.
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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> num = 0
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<strong>Output:</strong> 0
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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>0 <= num <= 2<sup>31</sup> - 1</code></li>
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</ul>
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<p> </p>
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<p><strong>Follow up:</strong> Could you do it without any loop/recursion in <code>O(1)</code> runtime?</p>
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