[Leetcode]17. Letter combinations of a phone number keyboard combination

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that number could repre Sent.

A mapping of Digit to letters (just as on the telephone buttons) is given below. Note that 1 does is not a map to any letters.

Example:

Input: "Output":["ad", "AE", "AF", "BD", "Be", "BF", "CD", "CE", "CF"].

Note:

Although the above answer is in lexicographical order, your answer could are in any order you want.

Test instructions

Given a string of numbers, see how many of the corresponding letter strings.

Ideas:

Assumption:

The legitimacy of the string, does it contain a number 1? If so, how do I deal with it? Similarly, does the input consider * or #?

How does an empty string work?

In what order are multiple solutions returned?

With the interviewer walk through:

Take "All" for example:

When index = 0, pointing to ' 2 ' in "23"

String letters = "ABC"

For each char in letters,

Add to Path

Move index forward, pointing to ' 3 ' in "recursively", and the helper function to add every char to the path

Code:

1 classSolution {2     Private Staticstring[] Keyboard =3             Newstring[]{"", "", "abc", "Def",//' 0 ', ' 1 ', ' 2 ',...4"Ghi", "JKL", "MnO", "PQRS", "TUV", "WXYZ" };5     6      Publiclist<string> lettercombinations (String digits) {//"All"7list<string> result =NewArraylist<>();8         if(digits.length () = = 0)returnresult;9Helper (digits, 0, ""), result);Ten         returnresult;  One     } A      -     Private voidHelper (String digits,intIndex, String Path, list<string>result) { -         if(Index = =digits.length ()) { the result.add (path); -             return; -         } -          +String letters = Keyboard[digits.charat (index)-' 0 '];  -          for(inti = 0; I < letters.length (); i++ ){ +             Charc =Letters.charat (i); AHelper (digits, index+1, path+c, result); at         } -     } -}

[Leetcode]17. Letter combinations of a phone number keyboard combination