- /*
- 17. 电话号码的字母组合
- 给定一个仅包含数字 2-9 的字符串, 返回所有它能表示的字母组合.
- 给出数字到字母的映射如下 (与电话按键相同). 注意 1 不对应任何字母.
- 输入:"23"
- 输出:["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
- 说明:
- 尽管上面的答案是按字典序排列的, 但是你可以任意选择答案输出的顺序.
- */
- /*
- 思路: 回溯搜索, 用 getString() 函数 取代 hashmap 速度更快
- */
- class Solution17Fix {
- private List<String> res = new LinkedList<>();
- private char[] solveArray;
- public List<String> letterCombinations(String digits) {
- if (digits == null || digits.length() == 0) {
- return new LinkedList<>();
- }
- solveArray = new char[digits.length()];
- search(0,digits);
- return res;
- }
- void search(int level, String digits) {
- if (level == digits.length()) {
- res.add(String.valueOf(solveArray));
- } else {
- String currString = getString(digits.charAt(level));
- for (int i = 0; i < currString.length(); i++) {
- solveArray[level] = currString.charAt(i);
- search(level + 1, digits);
- }
- }
- }
- String getString(char c) {
- switch (c) {
- case '2':
- return "abc";
- case '3':
- return "def";
- case '4':
- return "ghi";
- case '5':
- return "jkl";
- case '6':
- return "mno";
- case '7':
- return "pqrs";
- case '8':
- return "tuv";
- case '9':
- return "wxyz";
- default:
- return "";
- }
- }
- }
来源: http://www.bubuko.com/infodetail-2927183.html