[LeetCode] 249. Group Shifted Strings

ProblemGiven a string, we can “shift” each of its letter to its successive letter, for example: “abc” -> “bcd”. We can keep “shifting” which forms the sequence:“abc” -> “bcd” -> … -> “xyz"Given a list of strings which contains only lowercase alphabets, group all strings that belong to the same shifting sequence.Example:Input: [“abc”, “bcd”, “acef”, “xyz”, “az”, “ba”, “a”, “z”],Output: [ [“abc”,“bcd”,“xyz”], [“az”,“ba”], [“acef”], [“a”,“z”]]Solutionclass Solution { public List<List<String>> groupStrings(String[] strings) { Map<String, List<String>> map = new HashMap<>(); for (String str: strings) { StringBuilder sb = new StringBuilder(); for (int i = 1; i < str.length(); i++) { int diff = str.charAt(i)-str.charAt(i-1); if (diff < 0) diff += 26; sb.append(‘a’+diff); //***** ‘a’ ***** } String key = sb.toString(); map.putIfAbsent(key, new ArrayList<>()); map.get(key).add(str); } return new ArrayList<>(map.values()); }}//[“an”,“bcf”]//keys: 110, 98100//result: [[“an”],[“bcf”]]