java相关-回溯算法-电话号码的字母组合-力扣17

public class Main {
    public static List<String> result = new ArrayList<>();
    public static StringBuffer path = new StringBuffer();
    public static String[] ini = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

    public static void main(String[] args) {
        List<String> str = letterCombinations("2");
        System.out.println(str);
    }

    public static List<String> letterCombinations(String digits) {
        if (digits == null || digits.length() == 0) {
            return result;
        } else {
            int index = 0;
            backtracking(digits, index);
            return result;
        }
    }

    public static void backtracking(String digits, int index) {
        if (index == digits.length()) {
            result.add(path.toString());
            return;
        }
        int digit = Integer.valueOf(String.valueOf(digits.charAt(index)));
        String letter = ini[digit];
        for (int i = 0; i < letter.length(); i++) {
            path.append(String.valueOf(letter.charAt(i)));
            backtracking(digits, index + 1);
            path.deleteCharAt(path.length() - 1);
        }

    }
}