LeetCode Java First 400 题解-017

最新推荐文章于 2025-04-21 22:09:55 发布

原创最新推荐文章于 2025-04-21 22:09:55 发布 · 271 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#LeetCode #回溯法

刷题专栏收录该内容

34 篇文章

订阅专栏

本文介绍了一种解决电话号码字母组合问题的算法，通过回溯法实现，为给定的数字字符串返回所有可能的字母组合。算法首先定义了数字到字母的映射，然后使用递归方式结合之前的所有组合，生成新的结果。

Letter Combinations of a Phone Number Medium

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"

Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

public List<String> letterCombinations(String digits) {

    String letterSet[] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

    List<String> res = new ArrayList<String>();

    if (digits.length() == 0) {

        return res;

    }

    res.add("");

    for (int i = 0; i < digits.length(); i++)

        res = combination(letterSet[digits.charAt(i) - '0'], res);

    return res;

}



private static List<String> combination(String threeLetter, List<String> res) {

    List<String> result = new ArrayList<String>();

    for (int i = 0; i < threeLetter.length(); i++) {

        for (String str : res) {

            result.add(str + threeLetter.charAt(i));

        }

    }

    return result;

}