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1415. The k-th Lexicographical String of All Happy Strings of Length n

Difficulty Topics

Description

A happy string is a string that:

  • consists only of letters of the set ['a', 'b', 'c'].
  • 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.

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

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

 

Example 1:

Input: n = 1, k = 3
Output: "c"
Explanation: The list ["a", "b", "c"] contains all happy strings of length 1. The third string is "c".

Example 2:

Input: n = 1, k = 4
Output: ""
Explanation: There are only 3 happy strings of length 1.

Example 3:

Input: n = 3, k = 9
Output: "cab"
Explanation: 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 <= 10
  • 1 <= k <= 100

Solution

the-k-th-lexicographical-string-of-all-happy-strings-of-length-n.py
class Solution:
    def getHappyString(self, n: int, k: int) -> str:

        d = {"a":"bc", "b":"ac", "c":"ab"}
        q = collections.deque(["a","b","c"])

        while len(q[0]) < n:
            v = q.popleft()

            for u in d[v[-1]]:
                q.append(v+u)

        return q[k-1] if len(q) >= k else ""