题目描述

blablabla

样例

blablabla

算法1

Java 代码

class Solution {
    Map<Character, String> phone = new HashMap<>(){{
    put('2', "abc");
    put('3', "def");
    put('4', "ghi");
    put('5', "jkl");
    put('6', "mno");
    put('7', "pqrs");
    put('8', "tuv");
    put('9', "wxyz");
  }};
    List<String> res = new ArrayList<>();
    public List<String> letterCombinations(String digits) {
        if(digits == null || digits.length() == 0) return res;
        dfs(digits, 0, new String());
        return res;
    }

    private void dfs(String digits, int index, String s){
        if(index == digits.length()){
            res.add(s);
            return;
        }
        String letter = phone.get(digits.charAt(index));
        for(int i = 0; i < letter.length(); i++){
            String str = letter.substring(i, i + 1);
            dfs(digits, index + 1, s+str);
        }
    }
}