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trees/count_unival.py

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+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
+'''
+Given the root of a binary tree, return the number of uni-value subtrees.
+A uni-value subtree means all nodes of the subtree have the same value.
+'''
+ 
+def count_unival(root: Optional[TreeNode]) -> int:
+        
+        global count = 0
+        
+        def dfs(node):
+            
+            if not node:
+                return True
+        
+            is_uni_left = dfs(node.left)
+            is_uni_right = dfs(node.right)
+            
+            if is_uni_left and is_uni_right:
+                if node.left and node.left.val != node.val:
+                    return False
+                if node.right and node.right.val != node.val:
+                    return False
+            
+                self.count += 1
+                return True
+            
+            return False
+
+        dfs(root)
+        return count