【回溯】17. Letter Combinations of a Phone Number

采用回溯操作:

    vector<string> letterCombinations(string digits) {
     string table[11]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
     vector<string> res;
     string temp;
     if(digits.size()>0)
         find(res,digits,table,0,temp);
     return res;

    }

 void find(vector<string> &res,string &digits,string *table,int index,string &temp)
 {
 	if(index == digits.size())
 	{
 		res.push_back(temp);
 		return ;
 	}

 	for (int i = 0; i<table[digits[index]-'0'].size(); i++)
	{
        temp = temp + table[digits[index] - '0'][i];
		find(res, digits, table, index + 1, temp);
        temp.erase(temp.size()-1);
	}
 }