Check if All Leaf Nodes are at the Same Level in a Binary Tree

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

from collections import deque

def are_leaves_at_same_level(root):
    if not root:
        return True
    queue = deque([(root, 0)])
    leaf_level = -1
    while queue:
        node, level = queue.popleft()
        if not node.left and not node.right:
            if leaf_level == -1:
                leaf_level = level
            elif level != leaf_level:
                return False
        if node.left:
            queue.append((node.left, level + 1))
        if node.right:
            queue.append((node.right, level + 1))
    return True

# Example usage:
if __name__ == '__main__':
    # Construct binary tree:
    #         1
    #       /   \
    #      2     3
    #     / \     \
    #    4   5     6
    root = TreeNode(1, TreeNode(2, TreeNode(4), TreeNode(5)), TreeNode(3, None, TreeNode(6)))
    print(are_leaves_at_same_level(root))