Left-Leaning Red Black Tree Insertion in Java

RBT.java

    private static <Key extends Comparable<Key>, Value> boolean isRed(Node<Key, Value> root) {
        return root != null && root.isRed;
    }

    private static <Key extends Comparable<Key>, Value> int size(Node<Key, Value> root) {
        if (root == null) return 0;
        return 1 + size(root.left) + size(root.right);
    }

    private static <Key extends Comparable<Key>, Value> Node<Key, Value> leftRotate(Node<Key, Value> root) {
        var x = root.right;
        root.right = x.left;
        x.left = root;
        x.isRed = root.isRed;
        root.isRed = true;

        return x;
    }

    private static <Key extends Comparable<Key>, Value> Node<Key, Value> rightRotate(Node<Key, Value> root) {
        var x = root.left;
        root.left = x.right;
        x.right = root;
        x.isRed = root.isRed;
        root.isRed = true;

        return x;
    }

    private static <Key extends Comparable<Key>, Value> void colorFlip(Node<Key, Value> root) {
        root.isRed = true;
        root.left.isRed = false;
        root.right.isRed = false;
    }

    private static <Key extends Comparable<Key>, Value> Node<Key, Value> insert(Node<Key, Value> root, Key k, Value v) {
        if (root == null) return new Node<>(k, v, true);

        int comp = k.compareTo(root.key);


        if      (comp < 0)  root.left   = insert(root.left, k, v);
        else if (comp > 0)  root.right  = insert(root.right, k, v);
        else                root.value  = v;

        if (!isRed(root.left) && isRed(root.right)) root = leftRotate(root);
        if (isRed(root.left) && isRed(root.left.left)) root = rightRotate(root);
        if (isRed(root.left) && isRed(root.right)) colorFlip(root);

        root.size = size(root);

        return root;
    }