<!-- BEGIN COPY / PASTE -->
    import React, { useState, useMemo, useCallback } from 'react';

    const ExpensiveComponent = React.memo(({ data }) => {
      // Expensive calculations or rendering logic
      return <div>{data}</div>;
    });

    const App = () => {
      const [count, setCount] = useState(0);
      const [items, setItems] = useState([]);

      const addItem = useCallback(() => {
        setItems([...items, `Item ${items.length}`]);
      }, [items]);

      const expensiveCalculation = useMemo(() => {
        // Perform expensive calculation
        return items.length * 1000;
      }, [items]);

      return (
        <div>
          <button onClick={() => setCount(count + 1)}>Increment</button>
          <button onClick={addItem}>Add Item</button>
          <ExpensiveComponent data={expensiveCalculation} />
        </div>
      );
    };
    <!-- END COPY / PASTE -->