题目链接

17. 电话号码的字母组合

思路

使用 DFS 进行枚举。

代码

class Solution {
    private HashMap<Character, char[]> map = new HashMap<>();
    private List<String> result = new ArrayList<>();
    private char[] s;

    public List<String> letterCombinations(String digits) {
        if(digits.equals("")){
            return new ArrayList();
        }

        init();

        s = digits.toCharArray();
        int len = s.length;

        dfs(0, len, new StringBuilder());

        return result;
    }

    private void dfs(int index, int len, StringBuilder stringBuilder) {
        if(index == len){
            result.add(stringBuilder.toString());
            return;
        }

        System.out.println("index = " + index);
        char[] temp = map.get(s[index]);
        for(char c : temp){
            stringBuilder.append(c);
            dfs(index + 1, len, stringBuilder);
            stringBuilder.deleteCharAt(stringBuilder.length() - 1);
        }
    }

    void init(){
        map.put('2', new char[]{'a', 'b', 'c'});
        map.put('3', new char[]{'d', 'e', 'f'});
        map.put('4', new char[]{'g', 'h', 'i'});
        map.put('5', new char[]{'j', 'k', 'l'});
        map.put('6', new char[]{'m', 'n', 'o'});
        map.put('7', new char[]{'p', 'q', 'r', 's'});
        map.put('8', new char[]{'t', 'u', 'v'});
        map.put('9', new char[]{'w', 'x', 'y', 'z'});
    }
}