Space - Diana

lib/exercises.rb

@@ -1,19 +1,52 @@
 
 # This method will return an array of arrays.
 # Each subarray will have strings which are anagrams of each other
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(1)
 
 def grouped_anagrams(strings)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  string_hashmap = {}
+  strings.each do |string|
+    if string_hashmap[grouped_anagrams_helper(string)]
+      string_hashmap[grouped_anagrams_helper(string)] << string
+    else
+      string_hashmap[grouped_anagrams_helper(string)] = []
+      string_hashmap[grouped_anagrams_helper(string)] << string
+    end
+  end
+  return string_hashmap.values
+end
+
+def grouped_anagrams_helper(string)
+  return string.chars.sort.join
 end
 
 # This method will return the k most common elements
 # in the case of a tie it will select the first occuring element.
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n^2) in worst case because of the sorting to be done
+# Space Complexity: O(1)
 def top_k_frequent_elements(list, k)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  # build hashmap
+  num_hash = {}
+  list.each do |num|
+    if num_hash[num]
+      num_hash[num] += 1
+    else
+      num_hash[num] = 1
+    end
+  end
+
+  # convert hashmap to array
+  array_num_hash = num_hash.to_a
+
+  # sort by occurences
+  sorted_array_num_hash = array_num_hash.sort_by {|num| -num[1]}
+
+  # sorted elements only
+  sorted_numbers = sorted_array_num_hash.map{|num| num[0]}
+
+  # slice sorted array by k elements
+  return sorted_numbers.slice(0, k)
 end