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.
思考:DFS。
class Solution { public: void DFS(vector<string> &res,string ans,int dep,string digits,string dict[]) { if(dep==digits.size()) { res.push_back(ans); return; } for(int i=0;i<dict[digits[dep]-'0'].size();i++) { DFS(res,ans+dict[digits[dep]-'0'][i],dep+1,digits,dict); } } vector<string> letterCombinations(string digits) { vector<string> res; string ans=""; string dict[]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}; DFS(res,ans,0,digits,dict); return res; } };