The k-th Lexicographical String of All Happy Strings of Length n
A happy string is a string that:
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consists only of letters of the set ['a', 'b', 'c'] .
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s[i] != s[i + 1] for all values of i from 1 to s.length - 1 (string is 1-indexed).
For example, strings "abc", "ac", "b" and "abcbabcbcb" are all happy strings and strings "aa", "baa" and "ababbc" are not happy strings.
Provided two integers n and k , consider a list of all happy strings of length n sorted in lexicographical order.
Produce the kth string of this list or produce an empty string if there are less than k happy strings of length n .
Input: n = 1, k = 3
Output: "c"
Explanation: In this case, the list ["a", "b", "c"] contains all happy strings of length 1. The third string is "c".
Input: n = 1, k = 4
Output: ""
Explanation: In this case, there are only 3 happy strings of length 1.
Input: n = 3, k = 9
Output: "cab"
Explanation: In this case, 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"
Constraints
1 <= n <= 101 <= k <= 100
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