{ "data": { "question": { "questionId": "1516", "questionFrontendId": "1415", "boundTopicId": null, "title": "The k-th Lexicographical String of All Happy Strings of Length n", "titleSlug": "the-k-th-lexicographical-string-of-all-happy-strings-of-length-n", "content": "

A happy string is a string that:

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For example, strings "abc", "ac", "b" and "abcbabcbcb" are all happy strings and strings "aa", "baa" and "ababbc" are not happy strings.

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Given two integers n and k, consider a list of all happy strings of length n sorted in lexicographical order.

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Return the kth string of this list or return an empty string if there are less than k happy strings of length n.

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Example 1:

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\nInput: n = 1, k = 3\nOutput: "c"\nExplanation: The list ["a", "b", "c"] contains all happy strings of length 1. The third string is "c".\n
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Example 2:

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\nInput: n = 1, k = 4\nOutput: ""\nExplanation: There are only 3 happy strings of length 1.\n
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Example 3:

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\nInput: n = 3, k = 9\nOutput: "cab"\nExplanation: There are 12 different happy string of length 3 ["aba", "abc", "aca", "acb", "bab", "bac", "bca", "bcb", "cab", "cac", "cba", "cbc"]. You will find the 9th string = "cab"\n
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Constraints:

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Python 2.7.12.

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Node.js 16.13.2.

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