Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.
Example:
Input: "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.
AC code:
class Solution {
public:
vector<string> letterCombinations(string digits) {
vector<string> res;
if (digits.length() == 0) return res;
vector<string> num_map = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
res.push_back("");
for (int i = 0; i < digits.length(); ++i) {
vector<string> tem;
string str = num_map[digits[i]-‘0‘];
for (int j = 0; j < str.length(); ++j) {
for (int k = 0; k < res.size(); ++k) {
tem.push_back(res[k] + str[j]);
}
}
res = tem;
}
sort(res.begin(), res.end());
return res;
}
};
17. Letter Combinations of a Phone Number
原文：https://www.cnblogs.com/ruruozhenhao/p/9740902.html