17. Letter Combinations of a Phone Number

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"].

 

class Solution {
    void dfs(string mp[10], string& digits, int cur, vector<string>& ans, string path, bool vis[10][4]) {
        if(cur == digits.size()) {
            if(path.size() > 0)
                ans.push_back(path);
            return ;
        }
        int digit = digits[cur]-'0';
        string s = mp[digit];
        int n = s.size();
        for(int i=0; i<n; i++) {
            if(vis[cur][i]) continue;
            vis[cur][i] = true;
            path.push_back(s[i]);
            dfs(mp, digits, cur+1, ans, path, vis);
            vis[cur][i] = false;
            path.pop_back();
        }
    }
public:
    vector<string> letterCombinations(string digits) {
        string mp[] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
        vector<string> ans;
        bool vis[10][4] = {false};
        dfs(mp, digits, 0, ans, "", vis);
        return ans;
    }
};