diff --git a/src/my_project/interviews/amazon_high_frequency_23/common_algos/number_of_islands_round_4.py b/src/my_project/interviews/amazon_high_frequency_23/common_algos/number_of_islands_round_4.py
new file mode 100644
index 00000000..7da76e82
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/common_algos/number_of_islands_round_4.py
@@ -0,0 +1,39 @@
+from typing import List, Union, Collection, Mapping, Optional
+from collections import deque
+
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        """BFS approach - explores island level by level"""
+
+        if not grid: 
+            return 0
+        
+        rows, cols = len(grid), len(grid[0])
+        islands = 0
+
+        def bfs(r: int, c: int):
+            queue = deque([(r,c)])
+            grid[r][c] = '0'
+
+            while queue:
+                row, col = queue.popleft()
+
+                for dr, dc in [(1,0),(-1,0),(0,1),(0,-1)]:
+                    nr, nc = row + dr, col + dc 
+                    if (0 <= nr < rows and 0 <= nc < cols and grid[nr][nc] == '1'):
+                        grid[nr][nc] = '0'
+                        queue.append((nr, nc))
+
+        for r in range(rows):
+            for c in range(cols):
+                if grid[r][c] == '1':
+                    islands += 1
+                    bfs(r,c)
+
+        return islands
+    
+
+    def numIslands_DFS(grid: List[List[str]]) -> int:
+        """DFS approach - explores island depth-first"""
+
+        pass 
\ No newline at end of file
diff --git a/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_4.py b/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_4.py
new file mode 100644
index 00000000..e03fe46f
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_4.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_4.py b/src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_4.py
new file mode 100644
index 00000000..cad2b1e6
--- /dev/null
+++ b/src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_4.py
@@ -0,0 +1,22 @@
+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=r'[^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