adding updates

src/my_project/interviews/google_top_exercises/round_1/21_binary_tree_maximum_path_sum.py

@@ -0,0 +1,41 @@
+from typing import Optional
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+
+    def __init__(self):
+        self.max_sum = float('-inf')
+
+    def maxPathSum(self, root: Optional[TreeNode]) -> int:
+
+
+        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