LeetCode 17 电话号码的字母组合

编程语言：Java
题目链接：https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/
题解：水题
难度：Medium
结果：

class Solution {
    static List list;
    static String[][] strs={
        {"a","b","c"},
        {"d","e","f"},
        {"g","h","i"},
        {"j","k","l"},
        {"m","n","o"},
        {"p","q","r","s"},
        {"t","u","v"},
        {"w","x","y","z"}
    };

    public List letterCombinations(String digits) {
        list = new LinkedList<>();
        if(digits.length()!=0)
        dfs(digits, 0, new StringBuilder());
        return list;
    }

    private void dfs(String digits, int step, StringBuilder str) {
        if (step == digits.length()) {
            list.add(str.toString());
        } else {
            int x=digits.charAt(step)-'0'-2;
            for(int i=0;i
                str.append(strs[x][i]);
                dfs(digits, step+1, str);
                str.deleteCharAt(str.length()-1);
            }
        }
    }
}