package com.cool.hot100.backtracking;

import java.util.*;

/**
 * Created with IntelliJ IDEA.
 *
 * @Author: Cool
 * @Date: 2024/09/10/11:06
 * DayNumber 1
 * Hard 2
 * Level ?
 */
public class Num17 {

    List<String> res = new ArrayList<>();
    char[] chars;

    public List<String> letterCombinations(String digits) {
        if ("".equals(digits)) {
            return new ArrayList<>();
        }
        chars = new char[digits.length()];
        dfs(0, digits);
        return new ArrayList<>(res);
    }

    private void dfs(int index, String digits) {
        if (index >= digits.length()) {
            res.add(new String(chars));
            return;
        }
        String str = getLetter(digits.charAt(index)-'0');

        for (int i = 0; i < str.length(); i++) {
            chars[index] = str.charAt(i);
            dfs(index + 1, digits);

        }

    }

    private String getLetter(int num) {
        switch (num) {
            case 2:
                return "abc";
            case 3:
                return "def";
            case 4:
                return "ghi";
            case 5:
                return "jkl";
            case 6:
                return "mno";
            case 7:
                return "pqrs";
            case 8:
                return "tuv";
            case 9:
                return "wxyz";
            default:
                return "";
        }
    }

}