Diameter of a Binary Tree

python/problem_543/solution1.py

@@ -0,0 +1,30 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
+        diameter = 0
+
+        def longest_path(node):
+            # nonlocal to access the diameter when doing recursion
+            nonlocal diameter
+            # if no child
+            if not node:
+                return 0
+
+            # calculate the longest path for left and right
+            left_longest = longest_path(node.left)
+            right_longest = longest_path(node.right)
+
+            # check if its bigger than diameter
+            diameter = max(diameter, left_longest + right_longest)
+
+            # add the edge to parent while returning
+            return max(left_longest, right_longest) + 1
+
+        # do post-tree traversal
+        longest_path(root)
+        return diameter