17. Letter Combinations of a Phone Number - LeetCode Solution

class Solution:
    def letterCombinations(self, digits: str) -> List[str]:
        
        arr = ["asdf", "as", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"]
        ans = []


        def trav(t, i, string):


            if i == len(t):
                ans.append(string)
                return

            h = arr[int(t[i])]

            for j in range(len(h)):
                trav(t, i + 1, string + h[j])


        trav(digits, 0, "")
        
        if ans[0] == "":
            return []
        return ans