文章--LeetCode算法--LetterCombinationsofaPhoneNumber

目录

• LetterCombinationsofaPhoneNumber
  • 问题描述
  • 实例
  • 实现代码

LetterCombinationsofaPhoneNumber

问题描述

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.

实例

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

实现代码

    
    public class Solution {
        public List<String> letterCombinations(String digits) {
            Map<String, List<String>> digitalMap = new HashMap<String, List<String>>();
            digitalMap.put("2", new ArrayList<String>(Arrays.asList("a", "b", "c")));
            digitalMap.put("3", new ArrayList<String>(Arrays.asList("d", "e", "f")));
            digitalMap.put("4", new ArrayList<String>(Arrays.asList("g", "h", "i")));
            digitalMap.put("5", new ArrayList<String>(Arrays.asList("j", "k", "l")));
            digitalMap.put("6", new ArrayList<String>(Arrays.asList("m", "n", "o")));
            digitalMap.put("7", new ArrayList<String>(Arrays.asList("p", "q", "r", "s")));
            digitalMap.put("8", new ArrayList<String>(Arrays.asList("t", "u", "v")));
            digitalMap.put("9", new ArrayList<String>(Arrays.asList("w", "x", "y", "z")));
            List<String> resultList = new ArrayList<String>();
            getLetterCombinations(digits.toCharArray(), new StringBuilder(), 0, digitalMap, resultList);
            return resultList;
        }
        
        private static void getLetterCombinations(char[] c, StringBuilder sbSoFar, int curP, Map<String, List<String>> digitalMap, List<String> resultList) {
            if (curP == c.length) {
                if (sbSoFar.length() > 0)
                    resultList.add(sbSoFar.toString());
                return;
            }
            char cur = c[curP];
            for (String letter : digitalMap.get(String.valueOf(cur))) {
                StringBuilder sb = new StringBuilder();
                sb.append(sbSoFar);
                sb.append(letter);
                getLetterCombinations(c, sb, curP + 1, digitalMap, resultList);
            }
        }
    }