How to determine whether a binary tree is strict in Java ?

A binary tree is strict when all nodes have either two or zero child nodes. The following binary tree is an example of a strict binary tree:

Here are the algorithmic steps to check if a binary tree is strict:

1. A null node is a strict tree.
2. If the current node has exactly one child node, the tree is not strict.
3. If the current node has zero or two child nodes, then the tree is strict if both left and right child nodes are strict. The Java code looks like this:

The Java code looks like this:

public Boolean isStrictTree(TreeNode node) {
    if (node == null) {
        return true;
    }
    if ((node.left() == null && node.right() != null) || (node.left() != null && node.right() == null)) {
        return false;
    }
    return isStrictTree(node.left()) && isStrictTree(node.right());
}

You can play around with the code here.