[LeetCode] Letter Combinations of a Phone Number

题目

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"].

思路

这道题最朴素的思想就是，首先存储每个数字能表示的字符，然后按照给定的数字顺序遍历，这个遍历过程采取图论里面的深度优先搜索的策略。

代码

public class Solution {    public List<String> letterCombinations(String digits) {        List<String> result = new ArrayList<String>();        int len = digits.length();        if (len == 0)            return result;        String[] map = new String[] {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};        char[] combination = new char[digits.length()];        dfsCombine(digits, map, 0, combination, result);           return result;      }        public void dfsCombine(String digits, String[] map, int begin, char[] combination, List<String> result) {        if(begin == digits.length()) {              result.add(new String(combination));            return;          }          char c = digits.charAt(begin);          for(int i = 0; i < map[c - '0'].length(); i++) {            combination[begin] = map[c - '0'].charAt(i);              dfsCombine(digits, map, begin + 1, combination, result);          }      }}