Solution.java

class Solution {
    public List<String> invalidTransactions(String[] transactions) {
        Map<String, List<Item>> d = new HashMap<>();
        Set<Integer> idx = new HashSet<>();
        for (int i = 0; i < transactions.length; ++i) {
            var e = transactions[i].split(",");
            String name = e[0];
            int time = Integer.parseInt(e[1]);
            int amount = Integer.parseInt(e[2]);
            String city = e[3];
            d.computeIfAbsent(name, k -> new ArrayList<>()).add(new Item(time, city, i));
            if (amount > 1000) {
                idx.add(i);
            }
            for (Item item : d.get(name)) {
                if (!city.equals(item.city) && Math.abs(time - item.t) <= 60) {
                    idx.add(i);
                    idx.add(item.i);
                }
            }
        }
        List<String> ans = new ArrayList<>();
        for (int i : idx) {
            ans.add(transactions[i]);
        }
        return ans;
    }
}

class Item {
    int t;
    String city;
    int i;

    Item(int t, String city, int i) {
        this.t = t;
        this.city = city;
        this.i = i;
    }
}