class Solution {
public List<List<String>> groupAnagrams(String[] strs) {
// sort string, and use it as key, then put it into hash map (key = sorted string, value is list of Stings)
Map<String, List<String>> map = new HashMap<>();
for (String s : strs) {
char[] c = s.toCharArray();
Arrays.sort(c);
String sorted = new String(c);
List<String> list = map.getOrDefault(sorted, new ArrayList<>());
list.add(s);
map.put(sorted, list);
}
List<List<String>> result = new ArrayList<>();
Iterator<List<String>> iterator = map.values().iterator();
while(iterator.hasNext()) {
result.add(iterator.next());
}
return result;
}
}
Other solution might be to compile string into numerical string. First we would count all the letters, how many times they occur in the string? For example, "aab" would become a:2, b:1. Then we would create a template that would consist from all the letters (lets say only lower case is used): `2:1::::::::::::::::`. Then we can use these strings as a keys.