diff --git a/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_6.py b/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_6.py
new file mode 100644
index 00000000..e03fe46f
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_6.py
@@ -0,0 +1,16 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+
+        answer = dict()
+
+        for k, v in enumerate(nums):
+
+            if v in answer:
+                return [answer[v], k]
+            else: 
+                answer[target - v] = k
+
+        return []
\ No newline at end of file
diff --git a/src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_6.py b/src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_6.py
new file mode 100644
index 00000000..1ed43720
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_6.py
@@ -0,0 +1,23 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+import re
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+
+        # To lowercase
+        s = s.lower()
+
+        # Remove non-alphanumeric characters
+        s = re.sub(pattern='[^a-zA-Z0-9]', repl='', string=s)
+
+        # Determine if s is palindrome or not
+
+        len_s = len(s)
+
+        for i in range(len_s//2):
+
+            if s[i] != s[len_s - 1 - i]:
+                return False 
+            
+        return True 
\ No newline at end of file
diff --git a/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_adjacent_swapt_to_make_valid_array.py b/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_adjacent_swapt_to_make_valid_array.py
new file mode 100644
index 00000000..bb358b65
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_adjacent_swapt_to_make_valid_array.py
@@ -0,0 +1,17 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class Solution:
+    def minimumSwaps(self, nums: List[int]) -> int:
+
+        min_num = min(nums)
+        max_num = max(nums)
+
+        id_min  = nums.index(min_num)
+
+        new_nums = [min_num] + nums[:id_min] + nums[id_min + 1:]
+
+        id_max = new_nums[::-1].index(max_num)
+
+        return id_min + id_max
+
diff --git a/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_number_of_keypresses.py b/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_number_of_keypresses.py
new file mode 100644
index 00000000..ce4ea1e0
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/round_3/minimum_number_of_keypresses.py
@@ -0,0 +1,40 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+from collections import Counter
+
+class Solution:
+    def minimumKeypresses(self, s: str) -> int:
+        """
+        Greedy approach: Assign most frequent characters to 1-press slots
+        
+        Example: s = "apple"
+        Frequency: {'p': 2, 'a': 1, 'l': 1, 'e': 1}
+        
+        Assignment:
+        - 'p' (freq=2) → position 0 → 1 press → total: 2 * 1 = 2
+        - 'a' (freq=1) → position 1 → 1 press → total: 1 * 1 = 1
+        - 'l' (freq=1) → position 2 → 1 press → total: 1 * 1 = 1
+        - 'e' (freq=1) → position 3 → 1 press → total: 1 * 1 = 1
+        
+        Total: 2 + 1 + 1 + 1 = 5
+        """
+        
+        # Count character frequencies
+        freq = Counter(s)
+        print(freq)
+        
+        # Sort by frequency (descending) - greedy choice
+        counts = sorted(freq.values(), reverse=True)
+        print(counts)
+        
+        total_presses = 0
+        
+        # Calculate presses based on position
+        for position, frequency in enumerate(counts):
+            # Positions 0-8: 1 press (9 slots)
+            # Positions 9-17: 2 presses (9 slots)
+            # Positions 18-26: 3 presses (9 slots)
+            presses_per_char = (position // 9) + 1
+            total_presses += presses_per_char * frequency
+        
+        return total_presses    
\ No newline at end of file
diff --git a/src/my_project/interviews/top_150_questions_round_21/maximum_depth_binary_tree.py b/src/my_project/interviews/top_150_questions_round_21/maximum_depth_binary_tree.py
new file mode 100644
index 00000000..dbc93a50
--- /dev/null
+++ b/src/my_project/interviews/top_150_questions_round_21/maximum_depth_binary_tree.py
@@ -0,0 +1,17 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+
+        if not root: 
+            return 0
+        else: 
+            return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1
+        
diff --git a/tests/test_150_questions_round_21/test_maximum_depth_binary_tree_round_21.py b/tests/test_150_questions_round_21/test_maximum_depth_binary_tree_round_21.py
new file mode 100644
index 00000000..6e3a86db
--- /dev/null
+++ b/tests/test_150_questions_round_21/test_maximum_depth_binary_tree_round_21.py
@@ -0,0 +1,19 @@
+import unittest
+from src.my_project.interviews.top_150_questions_round_21\
+.maximum_depth_binary_tree import Solution, TreeNode
+
+class MaxDepthTreeTestCase(unittest.TestCase):
+
+    def test_max_depth_null(self):
+        solution = Solution()
+        tree = None
+        output = solution.maxDepth(root=tree)
+        target = 0
+        self.assertEqual(output, target)
+
+    def test_max_depth(self):
+        solution = Solution()
+        tree = TreeNode(1)
+        output = solution.maxDepth(root=tree)
+        target = 1
+        self.assertEqual(output, target)
\ No newline at end of file