kth lexigraphical

class Solution:
    def getHappyString(self, n: int, k: int) -> str:
        '''
        Input:
            n - the length of a happy string
            k - I want to return the 'k'th item
        Output:
            The 'k'th happy string of length 'n'
        Constraints:
            Only choose letters from {a,b,c}
            No subsequent letters in a row
        
        Approach:
            Choices
                Iterate through (a,b,c) on every level.
                    We don't use 'idx' and 'idx + 1'
            Bounding Function
                if i != 0 and partial[i] == partial[i - 1]:
                    Prune
            Goal:
                If len(partial) == n:
                    if counter == k: (goal 1)
                        return partial
                    result.append(partial) (goal 2)
            Output:
                If using goal 1, then just return this
                If using goal 2, return result[k - 1]
        Choices:
            for i in range(len(letters)):
                # Bounding function
                # check for duplicates
        '''