[LeetCode] Challenge log 17

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17. Letter Combinations of a Phone Number

It is a full permutation problem. DFS or BFS both ok.

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

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Example:

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Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:

Although the above answer is in lexicographical order, your answer could be in any order you want.

Soulution:
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class Solution:
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        if digits == "": return []
        dic = {'2':'abc', '3':'def', '4':'ghi', '5':'jkl', '6':'mno', '7':'pqrs', '8':'tuv', '9':'wxyz'}
        res = [x for x in dic[digits[0]]]
        for i in digits[1:]:
            temp = []
            for letter in dic[i]:
                temp += [x + letter for x in res]
            res = temp
        return res
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