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.
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.
回溯法递归调用即可：
class Solution {
public:
vector<string> letterCombinations(string digits) {
vector<string> num2string();
num2string[]="";
num2string[] = "";
num2string[] = "abc";
num2string[] = "def";
num2string[] = "ghi";
num2string[] = "jkl";
num2string[] = "mno";
num2string[] = "pqrs";
num2string[] = "tuv";
num2string[] = "wxyz";
vector<string> result;
string tmp="";
combination(digits,,tmp,num2string,result);
return result;
}
void combination(string &digits,int index,string tmp,vector<string> &num2string,vector<string> &result)
{
if(index==digits.length())
{
result.push_back(tmp);
return;
}
string mapString=num2string[digits[index]-''];
for(int i=;i<mapString.length();i++)
{
tmp.push_back(mapString[i]);
combination(digits,index+,tmp,num2string,result);
tmp.pop_back();
}
}
};