Given an array of strings, group anagrams together
Input: ["eat", "tea", "tan", "ate", "nat", "bat"]
Output:
[
["ate","eat","tea"],
["nat","tan"],
["bat"]
]
def groupAnagrams(strs):
ans = collections.defaultdict(list)
for s in strs:
ans[tuple(sorted(s))].append(s)
return ans.values()
- Algorithm Explain
- For each string in the list, sort it and convert it to a tuple like ('a', 'b', 't'), so for the string with the same letter will have the same tuple
- When try to store them into the dictionary, use the sorted tuple as the key so anagrams have the same key, could be append to the same list
- Dictionary "ans" looks like
{ ('a','b','t'): ['bat'], ('a','n','t'): ["nat","tan"], ('a','e','t'): ["ate","eat","tea"] }
- collection.defaultdict - create a dictionary and by given (list), it means the value will be a list. So for every key in this dictionay, its value will be a list, then there is no need to declare the list when access to the key, could use append directly
- difference between sorted() and .sort - "sorted()" will not modify the original string while ".sorted" will. Can sort list, tuple, string. Order based on "reverse=True or False"
- python dictionary method
- "dict.values()" returns a list of all values
- "dict.keys()" returns a list of all keys
- "dict.items()" returns a list of (key, value) tuples
class Solution {
public List<List<String>> groupAnagrams(String[] strs) {
if (strs.length == 0) return new ArrayList();
Map<String, List> ans = new HashMap<String, List>();
for (String s : strs) {
char[] ca = s.toCharArray();
Arrays.sort(ca);
String key = String.valueOf(ca);
if (!ans.containsKey(key)) ans.put(key, new ArrayList());
ans.get(key).add(s);
}
return new ArrayList(ans.values());
}
}
- Java ArrayList - The ArrayList class is a resizable array, while elements can be added and removed from an ArrayList whenever you want
- Java Map, Java HashMap - <data_type_of_the_key, data_type_of_the_value>
- toCharArray - convert the string to an character array; String.valueOf - return the string representation of the char array argument