leetCode:Letter Combinations of a Phone Number

题目

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"].

题目分析

输入若干个数字，将其对应的字母组合为若干个输出字符串

思路

用数组建立一张表，将每个数字对应的字符串存储起来。①逐个分析输入的每个字符，获得对应的字符串，再将字符串的每个字符逐次加入到之前的每个结果中，获得新的结果集。重复①步骤，直到分析完成。

AC代码

public class Solution {    public List<String> letterCombinations(String digits) {    if(digits == null || digits.isEmpty()){        return new ArrayList<String>();    }    List<String> result = new ArrayList<>();    result.add("");    String[] numToString = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};    for(int i = 0; i < digits.length(); i++){        List<String> res = new ArrayList<>();        String temp = numToString[Integer.parseInt(digits.charAt(i)+"")];        for(int j = 0; j < result.size(); j++){            for(int k = 0; k < temp.length(); ++k){                res.add(result.get(j) + temp.charAt(k));            }        }        result = res;    }    return result;    }}