[LeetCode][Java] Letter Combinations of a Phone Number

標籤：leetcode   java   letter combinations   

題目：

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"].

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

題意：

給定一個數字字串，返回這個數字能代表的所有的字母的組合。

數字對字母的映射如所示（就在電話的按鍵中）

Input:Digit string "23"Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

返回的結果可以按照任意的順序。

演算法分析：

 * 思路:


 *比如“234”這個字串，我可以先將0...1的所有排列找到-->{"a", "b", "c"}


 *再進一步將0...2的所有排列找到-->{"ad", "ae","af", "bd", "be", "bf", "cd", "ce", "cf"}


 *如此迴圈...直到字串末尾。實現如下

AC代碼：

public class Solution {    public  ArrayList<String> letterCombinations(String digits)     {    ArrayList<String> res=new ArrayList<String>();    String charmap[] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};    if (digits.length()==0) return res;    res.add("");        for (int i = 0; i < digits.length(); i++)        {          ArrayList<String> tempres=new ArrayList<String>();           String chars = charmap[digits.charAt(i) - '0'];          for (int c = 0; c < chars.length();c++)          {            for (int j = 0; j < res.size();j++)              tempres.add(res.get(j)+chars.charAt(c));          }            res = tempres;        }        return res;    }}

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[LeetCode][Java] Letter Combinations of a Phone Number