动态线段树

class CountIntervals {
    Node root;

    public CountIntervals() {
        root = new Node(1, (int)1e9);
    }

    public void add(int left, int right) {
        root.update(root, left, right);
    }

    public int count() {
        return root.val;
    }
}

class Node {
    int left;
    int right;
    int val;
    int mark;
    Node leftNode;
    Node rightNode;

    public Node(int l, int r) {
        left = l;
        right = r;
    }

    public Node getLeftNode() {
        if (leftNode == null) {
            leftNode = new Node(left, left + (right - left) / 2);
        }
        return leftNode;
    }

    public Node getRightNode() {
        if (rightNode == null) {
            rightNode = new Node(left + (right - left) / 2 + 1, right);
        }
        return rightNode;
    }

    public void update(Node node, int lo, int hi) {
        if (node.left > hi || node.right < lo) {
            return;
        }
        if (node.left >= lo && node.right <= hi) {
            node.mark = 1;
        } else {
            update(node.getLeftNode(), lo, hi);
            update(node.getRightNode(), lo, hi);
        }
        if (node.mark > 0) {
            node.val = node.right - node.left + 1;
        } else {
            node.val = node.getLeftNode().val + node.getRightNode().val;
        }
    }
}