Invalid Transactions LeetCode solution in Java

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class Solution {
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  public List<String> invalidTransactions(String[] transactions) {
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    Map<String, List<Transaction>> nameToTransaction = new HashMap<>();
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    for (int i = 0; i < transactions.length; i++) {
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      Transaction t = new Transaction(transactions[i], i);
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      nameToTransaction.putIfAbsent(t.name, new ArrayList<>());
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      nameToTransaction.get(t.name).add(t);
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    }
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    List<String> invalid = new ArrayList<>();
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    for (List<Transaction> list : nameToTransaction.values()) {
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      for (Transaction t : list) {
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        if (t.isInvalidAmount()) invalid.add(transactions[t.id]);
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        else {
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          for (Transaction otherT : list) {
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            if (t.isInvalidCity(otherT)) {
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              invalid.add(transactions[t.id]);
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              break;
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            }
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          }
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        }
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      }
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    }
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    return invalid;
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  }
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}
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class Transaction {
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  String name, city;
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  int time, amount, id;
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  Transaction(String s, int id) {
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    this.id = id;
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    String[] split = s.split(",");
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    name = split[0];
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    time = Integer.parseInt(split[1]);
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    amount = Integer.parseInt(split[2]);
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    city = split[3];
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  }
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  boolean isInvalidAmount() {
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    return this.amount > 1000;
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  }
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  boolean isInvalidCity(Transaction t) {
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    return !city.equals(t.city) && Math.abs(t.time - time) <= 60;
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  }
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}