public static Map<String, Double> calculateNetBalances(List<Expense> expenses) {
    Map<String, Double> netBalances = new HashMap<>();

    for (Expense expense : expenses) {
        String paidBy = expense.paidBy;

        // Total amount paid by this user (credited)
        double totalAmount = 0;
        for (ExpenseSplit split : expense.splits) {
            totalAmount += split.amount;
        }

        // Credit the payer
        netBalances.put(paidBy, netBalances.getOrDefault(paidBy, 0.0) + totalAmount);

        // Debit each participant
        for (ExpenseSplit split : expense.splits) {
            netBalances.put(split.user, netBalances.getOrDefault(split.user, 0.0) - split.amount);
        }
    }

    return netBalances;
}