diff --git a/hash_practice/exercises.py b/hash_practice/exercises.py
index 48bf95e..9cb0835 100644
--- a/hash_practice/exercises.py
+++ b/hash_practice/exercises.py
@@ -2,18 +2,40 @@
 def grouped_anagrams(strings):
     """ 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)
     """
-    pass
+    anagrams_map = {}
+    for word in strings:
+        sorted_word = "".join(sorted(word))
+        if sorted_word not in anagrams_map:
+            anagrams_map[sorted_word] = [word]
+        else:
+            anagrams_map[sorted_word].append(word)
+    return list(anagrams_map.values())
+
 
 def top_k_frequent_elements(nums, k):
     """ 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)
+        Space Complexity: O(n)
     """
-    pass
+    frequency_hash = {}
+    most_frequent_items = []
+    if len(nums) == 0:
+        return []
+    for item in nums:
+        if item in frequency_hash:
+            frequency_hash[item] += 1
+        else:
+            frequency_hash[item] = 1
+    
+    for i in range(k):
+        highest_frequency = max(frequency_hash, key = lambda num: frequency_hash[num])
+        most_frequent_items.append(highest_frequency) 
+        frequency_hash.pop(highest_frequency)
+    return most_frequent_items
 
 
 def valid_sudoku(table):
@@ -22,8 +44,52 @@ def valid_sudoku(table):
         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: O(n^2)
+        Space Complexity: O(n^2)
     """
-    pass
+    
+    #row
+    for row in range(9):
+        row_map = {}
+        for column in range(9):
+            tile = table[row][column]
+            if tile == ".":
+                continue
+            elif tile not in row_map:
+                row_map[tile] = 1
+            else:
+                return False
+
+    #column
+    for column in range(9):
+        column_map = {}
+        for row in range(9):
+            tile = table[row][column]
+            if tile == ".":
+                    continue
+            elif tile not in column_map:
+                column_map[tile] = 1
+            else:
+                return False
+
+    #sub-boxes
+    def squares(R, C):
+        squares_map = {}
+        for row in range(R, R+3):
+            for column in range(C, C+3):
+                tile= table[row][column]
+                if tile == ".":
+                    continue
+                elif tile not in squares_map:
+                    squares_map[tile] = 1             
+                else:
+                    return False
+        return True
+    for row in range(0,9,3):
+        for column in range(0,9,3):
+            if not squares(row, column):
+                return False
+    return True
+
+