Description
Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
Example 1:
Input: digits = "23" Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
Example 2:
Input: digits = "" Output: []
Example 3:
Input: digits = "2" Output: ["a","b","c"]
Constraints:
0 <= digits.length <= 4digits[i]is a digit in the range['2', '9'].
Solution
Python3
class Solution:
def letterCombinations(self, digits: str) -> List[str]:
if not digits: return []
N = len(digits)
res = []
words = {
"2": "abc",
"3": "def",
"4": "ghi",
"5": "jkl",
"6": "mno",
"7": "pqrs",
"8": "tuv",
"9": "wxyz"
}
def backtrack(index, curr):
if index == N:
res.append(curr)
return
for char in words[digits[index]]:
backtrack(index + 1, curr + char)
backtrack(0, "")
return res