{ "data": { "question": { "questionId": "258", "questionFrontendId": "258", "boundTopicId": null, "title": "Add Digits", "titleSlug": "add-digits", "content": "

Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.

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Example 1:

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\nInput: num = 38\nOutput: 2\nExplanation: The process is\n38 --> 3 + 8 --> 11\n11 --> 1 + 1 --> 2 \nSince 2 has only one digit, return it.\n
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Example 2:

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\nInput: num = 0\nOutput: 0\n
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Constraints:

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Follow up: Could you do it without any loop/recursion in O(1) runtime?

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