Letter Combinations of a Phone Number-白红宇

Letter Combinations of a Phone Number

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发布时间：2019-05-25

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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"].

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

Java代码：

public class Solution {          Map
     
      
       > map;    public List
       
         letterCombinations(String digits) {        map = new HashMap
        
         
          >();        this.map.put(2,new ArrayList
          
           (Arrays.asList("a","b","c"))); this.map.put(3,new ArrayList
           
            (Arrays.asList("d","e","f"))); this.map.put(4,new ArrayList
            
             (Arrays.asList("g","h","i"))); this.map.put(5,new ArrayList
             
              (Arrays.asList("j","k","l"))); this.map.put(6,new ArrayList
              
               (Arrays.asList("m","n","o"))); this.map.put(7,new ArrayList
               
                (Arrays.asList("p","q","r","s"))); this.map.put(8,new ArrayList
                
                 (Arrays.asList("t","u","v"))); this.map.put(9,new ArrayList
                 
                  (Arrays.asList("w","x","y","z"))); return comb(digits); } public List
                  
                    comb(String digits) { List
                   
                     result = new LinkedList
                    
                     (); if(digits.length() == 0) { result.add(new String("")); } else if(digits.length() == 1) { List
                     
                       ret = new LinkedList
                      
                       (); for(String c:map.get(Integer.parseInt(digits))) ret.add(c); return ret; } else { for(String s : comb(digits.substring(1))) { for(String c:map.get(Integer.parseInt(digits.substring(0,1)))) result.add(c + s); } } return result; } }