LeetCode 17 Letter Combinations of a Phone Number

17. Letter Combinations of a Phone Number

Total Accepted: 76019 Total Submissions: 267108 Difficulty: Medium

Given a digit string, 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.

Input:Digit string "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.

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排列组合

先打个表，然后枚举即可

class Solution {
public:
    vector<string> letterCombinations(string digits)
    {
        vector<string> ret;
        if(digits == "")
                return ret;
        ret.push_back("");
        string dict[]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
        for(int i = 0; i < digits.size(); i ++)
        {
                int size = ret.size();
                for(int j = 0; j < size; j ++)
                {
                        string cur = ret[0];
                        ret.erase(ret.begin());
                        for(int k = 0; k < dict[digits[i]-'0'].size(); k ++)
                                ret.push_back(cur + dict[digits[i]-'0'][k]);
                }
        }
        return ret;
    }
};