diff --git a/lib/exercises.rb b/lib/exercises.rb
index 2cb2bfa..d38b641 100644
--- a/lib/exercises.rb
+++ b/lib/exercises.rb
@@ -1,20 +1,64 @@
-
-
 # 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(n)
 
 def grouped_anagrams(strings)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  return [] if strings.empty?
+
+  anagram_hash = Hash.new()
+    strings.each do |string|
+      word_array = string.split("").sort
+      if anagram_hash.include?(word_array)
+        anagram_hash[word_array] << string
+      else
+        anagram_hash[word_array] = [string]
+      end
+    end
+
+    result = []
+    anagram_hash.each do |key, value|
+      result << value
+    end
+    return result
+
 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: ?
+# in the case of a tie it will select the first occurring element.
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def top_k_frequent_elements(list, k)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  return [] if list.empty?
+  return list if list.length == 1
+
+  element_count = Hash.new()
+
+  list.each do |element|
+    if element_count[element]
+      element_count[element] += 1
+    else
+      element_count[element] = 1
+    end
+  end
+
+  result = []
+
+  k.times do |i|
+      count = 0
+      frequent_element = nil
+      element_count.each do |element, frequency|
+        if frequency > count
+          count = frequency
+          frequent_element = element
+        end
+      end
+      result << frequent_element
+      element_count[frequent_element] = 0 if frequent_element
+    end
+
+  return result
+
 end
 
 
@@ -23,8 +67,73 @@ def top_k_frequent_elements(list, k)
 #   Each element can either be a ".", or a digit 1-9
 #   The same digit cannot appear twice or more in the same 
 #   row, column or 3x3 subgrid
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: I have no idea...O(n^2) since I have nested loops?
+# Space Complexity: O(n)
 def valid_sudoku(table)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
-end
\ No newline at end of file
+
+  return true if in_row?(table) && in_column?(table) && in_box?(table)
+
+  return false
+
+end
+
+  def in_row?(table)
+    table.length.times do |row|
+        sudoku_hash = Hash.new()
+        table.length.times do |i|
+
+          if sudoku_hash[table[row][i]]
+            return false
+          end
+
+          if table[row][i] != '.'
+          sudoku_hash[table[row][i]] = 1
+          end
+
+        end
+    end
+  end
+
+  # Checks whether there is any
+  # duplicate in current column or not.
+  def in_column?(table)
+
+    table.length.times do |col|
+      column_hash = Hash.new()
+
+      table.length.times do |i|
+
+        if column_hash[table[i][col]]
+          return false
+        end
+        if table[i][col] != '.'
+          column_hash[table[i][col]] = 1
+        end
+      end
+    end
+  end
+
+  # Checks whether there is any duplicate
+  # in current 3×3 box or not.
+  def in_box?(table)
+
+  # formula from https://stackoverflow.com/questions/41020695/how-do-i-split-a-9x9-array-into-9-3x3-components
+  grids = table.each_slice(3).map{|strip| strip.transpose.each_slice(3).map{|chunk| chunk.transpose}}.flatten(1)
+
+  grids.each do |box|
+      box_hash = Hash.new()
+      3.times do |row|
+        3.times do |col|
+           current = box[row][col]
+            if box_hash[current]
+              return false
+            end
+            if current != '.'
+              box_hash[current] = 1
+            end
+        end
+      end
+
+    end
+
+end
diff --git a/test/exercises_test.rb b/test/exercises_test.rb
index a649110..710370e 100644
--- a/test/exercises_test.rb
+++ b/test/exercises_test.rb
@@ -68,7 +68,7 @@
     end
   end
 
-  xdescribe "top_k_frequent_elements" do
+  describe "top_k_frequent_elements" do
     it "works with example 1" do
       # Arrange
       list = [1,1,1,2,2,3]
@@ -131,7 +131,7 @@
 
   end
 
-  xdescribe "valid sudoku" do
+  describe "valid sudoku" do
     it "works for the table given in the README" do
       # Arrange
       table = [