<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>

class Solution {
private:
  vector<string> split(string str, string delim) {
    vector<string> result { };
    string::size_type start { 0 }, pos { 0 };
    string part { };

    while ((pos = str.find(delim, start)) != string::npos) {
      part = str.substr(start, pos - start);
      start = pos + delim.size();
      result.push_back(part);
    }
    result.push_back(str.substr(start));

    return result;
  }
  
public:
  vector<string> invalidTransactions(vector<string>& transactions) {
    vector<string> result { };    

    unordered_map<string, unordered_map<int, unordered_set<string>>> trans { };
    for (auto const& t : transactions) {
      auto ss { split(t, ",") };
      trans[ss[0]][stoi(ss[1])].insert(ss[3]);
    }

    for (auto const& t : transactions) {
      auto ss { split(t, ",") };
      if (stoi(ss[2]) > 1000) { result.push_back(t); continue; }
      if (trans.find(ss[0]) == trans.end()) { continue; }
      for (int i { stoi(ss[1]) - 60 }; i < stoi(ss[1]) + 61; ++i) {
        if (trans[ss[0]].find(i) != trans[ss[0]].end()) {
          if (trans[ss[0]][i].size() > 1 || trans[ss[0]][i].find(ss[3]) == trans[ss[0]][i].end()) {
            result.push_back(t);
            break;
          } 
        }
      }
    }

    return result;
  }
};
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