[*leetcode 17] 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.

[Solution]

递归求解。

const string dict[10] = {"", " ", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
vector<string> letterCombinations(string digits)
{
vector<string> result;
if (digits.size() == 0)
return result;
string line;
proceed(result, line, digits, 0);

return result;
}

void proceed(vector<string> &result, string &line, const string &digits, int steps)
{
if(steps == digits.size())
{
result.push_back(line);
return;
}

for (int i = 0; i < dict[digits[steps] - '0'].size(); i++)
{
line.push_back(dict[digits[steps] - '0'][i]);
proceed(result, line, digits, steps + 1);
line.pop_back();
}
}