Create Check Completeness of a Binary Tree.py

Author: anthonyzhub

Check Completeness of a Binary Tree.py

@@ -0,0 +1,68 @@
+# https://leetcode.com/problems/check-completeness-of-a-binary-tree/
+
+# 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
+
+from collections import deque
+
+class Solution:
+    
+    def isCompleteTree(self, root: Optional[TreeNode]) -> bool:
+        
+        """
+        OBJECTIVE: Return true if given binary tree is complete. If not, return false
+        
+        NOTE: A complete binary tree only has NULL nodes at the bottom, far-right side of the tree. I.e, if a tree has N nodes, then N - 1 nodes can't be null!
+        
+        Time Complexity: O(n) where n = # of nodes because the tree is being traversed once through breadth-first search
+        
+        Space Complexity: O(n) where n = # of nodes because all the nodes are being added to a queue during a breadth-first search
+        """
+        
+        # If root is empty or by itself, return true
+        if root is None or (root.left == root.right == None):
+            return True
+        
+        # Use bfs() to traverse tree
+        queue = deque([root])
+        discoveredNull = False # <= Create a variable to determine if a None node was discovered
+        
+        while queue:
+            
+            # Pop first element from queue
+            popped = queue.popleft()
+            
+            # Check if there's a left child
+            if popped.left:
+                
+                # If a null node was previously discovered, return false
+                if discoveredNull:
+                    return False
+                
+                # Add left child to queue
+                queue.append(popped.left)
+                
+            # If left child is null, set boolean variable to true
+            else:
+                discoveredNull = True
+            
+            # Check if there's a right child
+            if popped.right:
+                
+                # If a null node was previously discovered, return false
+                if discoveredNull:
+                    return False
+                
+                # Add right child to queue
+                queue.append(popped.right)
+                
+            # If right child is null, set boolean variable to true
+            else:
+                discoveredNull = True
+        
+        # If function is still continuing, then tree is complete
+        return True