Find Second Largest - Iterative

SecondLargest.java

private static int findLargest(BinaryTreeNode rootNode) {
    BinaryTreeNode current = rootNode;
    while (current.right != null) {
        current = current.right;
    }
    return current.value;
}

public static int findSecondLargest(BinaryTreeNode rootNode) {
    if (rootNode == null || (rootNode.left == null
            && rootNode.right == null)) {
        throw new IllegalArgumentException("Tree must have at least 2 nodes");
    }

    BinaryTreeNode current = rootNode;

    while (true) {

        // case: current is largest and has a left subtree
        // 2nd largest is the largest in that subtree
        if (current.left != null && current.right == null) {
            return findLargest(current.left);
        }

        // case: current is parent of largest, and largest has no children,
        // so current is 2nd largest
        if (current.right != null &&
                current.right.left == null &&
                current.right.right == null) {
            return current.value;
        }

        current = current.right;
    }
}