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Group Anagrams

To solve this problem, we can use a hash map to group anagrams together. We will iterate through the array of strings and sort each string in alphabetical order.

We will then use the sorted string as a key in our hash map and store the original unsorted string as a value in an array. If we encounter a new string that has the same sorted form as a previous string, we can simply append it to the array associated with that key.

After we have processed all the strings, we can return the values of the hash map as an array of arrays.

Here's the JavaScript code to solve the problem:

function groupAnagrams(strs) {
  const map = new Map();
  for (let str of strs) {
    const sortedStr = str.split("").sort().join("");
    if (map.has(sortedStr)) {
      map.get(sortedStr).push(str);
    } else {
      map.set(sortedStr, [str]);
    }
  }
  return Array.from(map.values());
}

The time complexity of this solution is O(n * k log k), where n is the length of the input array and k is the maximum length of a string in the array. This is because we are iterating through each string in the array and sorting it, which takes O(k log k) time.

The space complexity of this solution is O(n * k), since we need to store all the strings and their sorted forms in the hash map.