<p>A transaction is possibly invalid if:</p>

<ul>
	<li>the amount exceeds <code>$1000</code>, or;</li>
	<li>if it occurs within (and including) <code>60</code> minutes of another transaction with the <strong>same name</strong> in a <strong>different city</strong>.</li>
</ul>

<p>You are given an array of strings <code>transaction</code> where <code>transactions[i]</code> consists of comma-separated values representing the name, time (in minutes), amount, and city of the transaction.</p>

<p>Return a list of <code>transactions</code> that are possibly invalid. You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> transactions = [&quot;alice,20,800,mtv&quot;,&quot;alice,50,100,beijing&quot;]
<strong>Output:</strong> [&quot;alice,20,800,mtv&quot;,&quot;alice,50,100,beijing&quot;]
<strong>Explanation:</strong> The first transaction is invalid because the second transaction occurs within a difference of 60 minutes, have the same name and is in a different city. Similarly the second one is invalid too.</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> transactions = [&quot;alice,20,800,mtv&quot;,&quot;alice,50,1200,mtv&quot;]
<strong>Output:</strong> [&quot;alice,50,1200,mtv&quot;]
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> transactions = [&quot;alice,20,800,mtv&quot;,&quot;bob,50,1200,mtv&quot;]
<strong>Output:</strong> [&quot;bob,50,1200,mtv&quot;]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>transactions.length &lt;= 1000</code></li>
	<li>Each <code>transactions[i]</code> takes the form <code>&quot;{name},{time},{amount},{city}&quot;</code></li>
	<li>Each <code>{name}</code> and <code>{city}</code> consist of lowercase English letters, and have lengths between <code>1</code> and <code>10</code>.</li>
	<li>Each <code>{time}</code> consist of digits, and represent an integer between <code>0</code> and <code>1000</code>.</li>
	<li>Each <code>{amount}</code> consist of digits, and represent an integer between <code>0</code> and <code>2000</code>.</li>
</ul>

struct Transaction {
  string name;
  int time;
  int amount;
  string city;
};

class Solution {
 public:
  vector<string> invalidTransactions(vector<string>& transactions) {
    vector<string> ans;
    unordered_map<string, vector<Transaction>> nameToTransactions;

    for (const string& t : transactions) {
      const Transaction transaction = getTransaction(t);
      nameToTransactions[transaction.name].push_back(transaction);
    }

    for (const string& t : transactions) {
      const Transaction currTransaction = getTransaction(t);
      if (currTransaction.amount > 1000) {
        ans.push_back(t);
      } else if (const auto it = nameToTransactions.find(currTransaction.name);
                 it != nameToTransactions.cend()) {
        // Iterate through all the transactions with the same name, check if
        // they're within 60 minutes in a different city.
        for (Transaction transaction : it->second)
          if (abs(transaction.time - currTransaction.time) <= 60 &&
              transaction.city != currTransaction.city) {
            ans.push_back(t);
            break;
          }
      }
    }

    return ans;
  }

 private:
  Transaction getTransaction(const string& t) {
    istringstream iss(t);
    vector<string> s(4, "");
    for (int i = 0; getline(iss, s[i++], ',');)
      ;
    return {s[0], stoi(s[1]), stoi(s[2]), s[3]};  // [name, time, amount, city]
  }
};
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