import React, { useMemo, useState } from 'react'; const initial = [ { id: 'r1', name: 'React Basics', qty: 1 }, { id: 'r2', name: 'Hooks', qty: 2 } ]; export default function App() { const [items, setItems] = useState(initial); function change(id, delta) { setItems((prev) => { const next = prev.map((x) => (x.id === id ? { ...x, qty: x.qty + delta } : x)); return next.filter((x) => x.qty > 0); }); } const total = useMemo(() => items.reduce((s, x) => s + x.qty, 0), [items]); return ( <div style={{ padding: 16, width: 520 }}> <h2 style={{ marginTop: 0 }}>meetcode cart</h2> <div style={{ color: '#555' }}>Total items: {total}</div> <ul style={{ marginTop: 12, paddingLeft: 18 }}> {items.map((it) => ( <li key={it.id} style={{ marginBottom: 10 }}> <strong>{it.name}</strong> — {it.qty} <div style={{ display: 'flex', gap: 8, marginTop: 6 }}> <button type='button' onClick={() => change(it.id, -1)} style={{ padding: '6px 10px', borderRadius: 12, border: '1px solid #ddd', background: '#fff' }}>-</button> <button type='button' onClick={() => change(it.id, +1)} style={{ padding: '6px 10px', borderRadius: 12, border: 0, background: '#0b5', color: '#fff' }}>+</button> </div> </li> ))} </ul> </div> ); }