check_completeness_of_a_binary_tree.py

'''
Given the root of a binary tree, determine if it is a complete binary tree.

In a complete binary tree, every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
'''


def isCompleteTree(self, root: TreeNode) -> bool:
        end = False
        queue = collections.deque([root])
        
        while queue:
            node = queue.popleft()
            
            if not node:
                end = True
            else:
                if end:
                    return False
                else:
                    queue.append(node.left)
                    queue.append(node.right)
        
        return True
      
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class Solution:
    def isCompleteTree(self, root: TreeNode) -> bool:
        have_null = False
        Q = [root]
        
        while Q:
            cur_node = Q.pop(0)
            if not cur_node: 
                have_null = True
                continue
            if have_null: return False
            Q.append(cur_node.left)
            Q.append(cur_node.right)
            
        return True