package LeetCode;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class LC_17 {
    static StringBuilder path = new StringBuilder();
    static List<String> res = new ArrayList<>();

    public static void main(String[] args) {
        letterCombinations("23");
    }

    public static List<String> letterCombinations(String digits) {
        if (digits == null || digits.length() == 0) return res;
        String[] key = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
        backtracking(digits, key, 0);
        System.out.println(res);
        return res;
    }

    public static void backtracking(String digits, String[] key, int startIndex) {
        if (path.length() == digits.length()) {
            res.add(path.toString());
            return;
        }
        String nowKey = key[digits.charAt(startIndex) - '0'];
        for (int i = 0; i < nowKey.length(); i++) {
            path.append(nowKey.charAt(i));
            backtracking(digits, key, startIndex + 1);
            path.deleteCharAt(path.length() - 1);
        }
    }
}