adding algo

src/my_project/interviews/amazon_high_frequency_23/common_algos/two_sum_round_2.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 []

src/my_project/interviews/amazon_high_frequency_23/common_algos/valid_palindrome_round_2.py

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+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 
+

src/my_project/interviews/top_150_questions_round_22/ex_75_binary_tree_maximum_path_sum.py

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+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 maxPathSum(self, root: Optional[TreeNode]) -> int:
+        self.max_sum = float('-inf')
+
+        def dfs(node: Optional[TreeNode]) -> int:
+            """
+            Returns the maximum path sum that can be extended to the parent.
+            Updates self.max_sum with the maximum path sum through this node.
+            """
+            if not node:
+                return 0
+
+            # Get maximum contribution from left and right subtrees
+            # Use max with 0 to ignore negative paths
+            left_max = max(0, dfs(node.left))
+            right_max = max(0, dfs(node.right))
+
+            # Maximum path sum through this node (can't be extended upward)
+            path_through_node = node.val + left_max + right_max
+
+            # Update global maximum
+            self.max_sum = max(self.max_sum, path_through_node)
+
+            # Return maximum path that can be extended to parent
+            # Can only choose one direction (left or right)
+            return node.val + max(left_max, right_max)
+
+        dfs(root)
+        return self.max_sum

src/my_project/interviews_typescript/top_150_questions_round_1/ex_75_binary_tree_maximum_path_sum.ts

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+import { TreeNode } from './TreeNode';
+
+function maxPathSum(root: TreeNode | null): number {
+    let maxSum = -Infinity;
+
+    function dfs(node: TreeNode | null): number {
+        /**
+         * Returns the maximum path sum that can be extended to the parent.
+         * Updates maxSum with the maximum path sum through this node.
+         */
+        if (!node) {
+            return 0;
+        }
+
+        // Get maximum contribution from left and right subtrees
+        // Use Math.max with 0 to ignore negative paths
+        const leftMax = Math.max(0, dfs(node.left));
+        const rightMax = Math.max(0, dfs(node.right));
+
+        // Maximum path sum through this node (can't be extended upward)
+        const pathThroughNode = node.val + leftMax + rightMax;
+
+        // Update global maximum
+        maxSum = Math.max(maxSum, pathThroughNode);
+
+        // Return maximum path that can be extended to parent
+        // Can only choose one direction (left or right)
+        return node.val + Math.max(leftMax, rightMax);
+    }
+
+    dfs(root);
+    return maxSum;
+}

tests/test_150_questions_round_22/test_75_binary_tree_maximum_path_sum_round_22.py

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+import unittest
+from typing import Optional, List
+from src.my_project.interviews.top_150_questions_round_22\
+.ex_75_binary_tree_maximum_path_sum import Solution, TreeNode
+
+
+class BinaryTreeMaximumPathSumTestCase(unittest.TestCase):
+
+    def test_example_1(self):
+        """
+        Input: root = [1,2,3]
+        Output: 6
+        Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.
+        """
+        solution = Solution()
+        tree = TreeNode(1, TreeNode(2), TreeNode(3))
+        output = solution.maxPathSum(root=tree)
+        self.assertEqual(output, 6)
+
+    def test_example_2(self):
+        """
+        Input: root = [-10,9,20,null,null,15,7]
+        Output: 42
+        Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.
+        """
+        solution = Solution()
+        tree = TreeNode(-10)
+        tree.left = TreeNode(9)
+        tree.right = TreeNode(20)
+        tree.right.left = TreeNode(15)
+        tree.right.right = TreeNode(7)
+        output = solution.maxPathSum(root=tree)
+        self.assertEqual(output, 42)