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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.
题目大意：给一组数字，按照电话键盘上的组合输出所有的可能。
解题思路：直接递归写DFS，输出所有组合。
import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class LetterCombinationsofaPhoneNumber { public static void main(String[] sure) { new LetterCombinationsofaPhoneNumber().letterCombinations("213"); } static Map<Character, String> mapping = new HashMap<>(); static { mapping.put(‘0‘, ""); mapping.put(‘1‘, ""); mapping.put(‘2‘, "abc"); mapping.put(‘3‘, "def"); mapping.put(‘4‘, "ghi"); mapping.put(‘5‘, "jkl"); mapping.put(‘6‘, "mno"); mapping.put(‘7‘, "pqrs"); mapping.put(‘8‘, "tuv"); mapping.put(‘9‘, "wxyz"); } public List<String> letterCombinations(String digits) { List<String> res = new ArrayList<>(); if (digits == null || digits.length() == 0) { return res; } combine(digits, "", res, digits.length()); System.out.println(res); return res; } private void combine(String digits, String tmp, List<String> res, int length) { if (length == 0) { res.add(tmp); return; } for (int i = 0; i < digits.length(); i++) { String val = mapping.get(digits.charAt(i)); if ("".equals(val)) { combine(digits.substring(i + 1), tmp, res, length - 1); } else { for (char c : val.toCharArray()) { combine(digits.substring(i + 1), tmp + c, res, length - 1); } } } } }
Letter Combinations of a Phone Number——LeetCode
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原文地址：http://www.cnblogs.com/aboutblank/p/4395968.html
