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[LeetCode] 17. Letter Combinations of a Phone Number

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.

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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.

 1 class Solution { 2     unordered_map<char, vector<string>> ht  = { 3              {0, {" "}}, {1, {""}}, {2, {"a", "b", "c"}}, {3, {"d", "e", "f"}}, 4              {4, {"g", "h", "i"}}, {5, {"j", "k", "l"}}, {6, {"m", "n", "o"}}, 5              {7, {"p", "q", "r", "s"}}, {8, {"t", "u", "v"}}, {9, {"w", "x", "y", "z"}}, 6     };        7 public: 8     vector<string> letterCombinations(string digits) { 9         vector<string> ret;10         int n = digits.size();11         12         if (n == 0) return ret;13     14         if (n == 1) return ht[digits[0]];15        16         vector<string> prev = letterCombinations(digits.substr(0, n - 1));17 18         for (auto s : prev){19             for (int i = 0; i < ht[digits[n-1]].size(); i++)20             ret.push_back(s+ht[digits[n-1]][i]);21         }22         23         return ret;24     }25 };

 

[LeetCode] 17. Letter Combinations of a Phone Number