门店经理视角下的零售数据分析分享

17. 电话号码的字母组合

回溯

class Solution {
    List<String> res = new ArrayList<>();
    String[] map = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

    public List<String> letterCombinations(String digits) {
        if(digits.length() == 0) return res;
        backtrack(digits, 0, "");
        return res;
    }

    void backtrack(String digits, int ind, String path){
        if(ind == digits.length()){
            res.add(path.toString());
            return;
        }

        String str = map[digits.charAt(ind) - '0'];
        for(char c : str.toCharArray()){
            backtrack(digits, ind + 1, path + c);
        }
    }
}