Letter Combinations of a Phone Number-白红宇

手机按键组合，回溯

Letter Combinations of a Phone Number

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"].

1 package com.rust.TestString; 2  3 import java.util.ArrayList; 4 import java.util.List; 5  6 public class LetterCombinationsofaPhoneNumber { 7     public static List
     
       letterCombinations(String digits) { 8          List
      
        result = new ArrayList
       
        (); 9          if (digits.equalsIgnoreCase("")) {10             return result;11         }12          String[] keys = new String[10];  13          keys[0] = "";  14          keys[1] = "";  15          keys[2] = "abc";  16          keys[3] = "def";  17          keys[4] = "ghi";  18          keys[5] = "jkl";  19          keys[6] = "mno";  20          keys[7] = "pqrs";  21          keys[8] = "tuv";  22          keys[9] = "wxyz";  23          char[] temp = new char[digits.length()];24          combine(keys, temp, digits, 0, result);25          return result;26     }27     public static void combine(String[] keys, char[] temp, String digits, int index, List
        
          res) {28         if (index == digits.length()) {29             res.add(new String(temp));30             return;  // get out now31         }32         char digitChar = digits.charAt(index);33         for (int i = 0; i < keys[digitChar - '0'].length(); i++) {  // scan char at keys[digitChar - '0']34             temp[index] = keys[digitChar - '0'].charAt(i);35             combine(keys, temp, digits, index + 1, res);36         }37  38     }39     public static void main(String args[]){40         List
         
           one = letterCombinations("");41         for (int i = 0; i < one.size(); i++) {42             System.out.print(one.get(i)+"  ");43         }44     }45 }