diff --git a/hash_practice/exercises.py b/hash_practice/exercises.py
index 48bf95e..01ab9d9 100644
--- a/hash_practice/exercises.py
+++ b/hash_practice/exercises.py
@@ -2,18 +2,50 @@
 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(nklog(k)), where k is the length of the string 
+        Space Complexity: O(log(n))
     """
-    pass
+    if not strings:
+        return []
+
+    result = {}
+    for word in strings:
+        key = ''.join(sorted(word))
+        if key in result:
+            result.get(key).append(word)
+        else:
+            result[key] = [word]
+    return result.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
+    if not nums:
+        return []
+    count = {}
+    frequency = [[] for i in range(len(nums)+1)]
+    for n in nums:
+        if n not in count:
+            count[n] = 0
+        count[n] += 1
+
+    for key, val in count.items():
+        frequency[val].append(key)
+    
+
+    result = []
+    for i in range(len(frequency)-1, 0, -1):
+        for n in frequency[i]:
+            result.append(n)
+            if len(result) == k:
+                return result
 
 
 def valid_sudoku(table):
@@ -22,8 +54,25 @@ 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: ?
-    """
-    pass
+        Time Complexity: o(n^2)
+        Space Complexity: O(n)
+#     """
+from collections import defaultdict     
+def validSudoku(board):
+    if board == None:
+        return None
+    N = 9
+    cols = defaultdict(set)
+    rows = defaultdict(set)
+    squares = defaultdict(set)
 
+    for row in range(9):
+        for col in range(9):
+            if board[row][col] == ".":
+                continue
+            if(board[row][col] in rows[row] or board[row][col] in cols[col] or board[row][col] in squares[(row // 3, col // 3)]):
+                return False
+            cols[col].add(board[row][col])
+            rows[row].add(board[row][col])
+            squares[(row // 3, col // 3)].add(board[row][col])
+    return True