class Solution:
    def letterCombinations(self, digits):
        if not digits:
            return []

        dictionario = {
        '2': 'abc',
        '3': 'def',
        '4': 'ghi',
        '5': 'jkl',
        '6': 'mno',
        '7': 'pqrs',
        '8': 'tuv',
        '9': 'wxyz',
      }
        queue = collections.deque()
        queue.append('')
        for char in digits:
            for i in range(len(queue)):
                s = queue.popleft()
                for c in dictionario[char]:
                    queue.append(s + c)

        return queue