Difficulty: 3
Frequency 3
Problem:
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.
Solution:
class Solution {
public:
string letters[10] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
vector<string> letterCombinations(string digits) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<string> answer;
vector<char> v_letters;
DFS (digits, 0, v_letters, answer);
return answer;
}
void DFS(string & digits, int i_level, vector<char> & v_letters, vector<string> & answer)
{
if (i_level==digits.size())
{
string str_letter;
for (int i = 0; i<v_letters.size(); i++)
{
str_letter += v_letters[i];
}
answer.push_back(str_letter);
return;
}
for (int i = 0; i<letters[digits[i_level]-'0'].size(); i++)
{
v_letters.push_back(letters[digits[i_level]-'0'][i]);
DFS(digits, i_level+1, v_letters, answer);
v_letters.pop_back();
}
}
};
Notes:
Just DFS, It is boring.