Array     C++     Hash Table     Medium     Python     Sorting     String    

Problem Statement:

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

 

Example 1:

Input: strs = ["eat","tea","tan","ate","nat","bat"]
Output: [["bat"],["nat","tan"],["ate","eat","tea"]]

Example 2:

Input: strs = [""]
Output: [[""]]

Example 3:

Input: strs = ["a"]
Output: [["a"]]

 

Constraints:

  • 1 <= strs.length <= 104
  • 0 <= strs[i].length <= 100
  • strs[i] consists of lowercase English letters.

Solution:

Basic idea is to match sorted version of string. Note that anagrams will have same result when sorted. So let us use this as a key for Hashmap.

C++:

 
class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        unordered_map<string, vector<string>> H;
        for (string str: strs)
        {
            string strsorted = str;
            sort(strsorted.begin(),strsorted.end());
            if (H.count(strsorted))
            {
                H[strsorted].push_back(str);
                continue;
            }
            H[strsorted] = {str};
        }
        vector<vector<string>>res;
        for (auto p: H) res.push_back(p.second);
        return res;
    }
};

Python:

 
class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        H = {}
        for str in strs:
            strsorted = ''.join(sorted(str))
            if strsorted in H:
                H[strsorted].append(str)
                continue
            H[strsorted] = [str];
        return list(H.values())