<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 {
public:
    struct model {
        string name="";
        string city="";
        int amt=0;
        int time=0;
        int ind;
    };
    
    vector<string> invalidTransactions(vector<string>& transactions) {
        int n = transactions.size();
        vector<string> ans;
        vector<model> vec;
        set<int> invalidIndices;  // To track invalid transactions and avoid duplicates

        // Parse each transaction into the model
        for (int i = 0; i < n; i++) {
            model v;
            string temp = transactions[i];
            int j = 0, m = temp.size();

            // Extract name
            while (temp[j] != ',') {
                v.name += temp[j];
                j++;
            }
            j++;  // Skip the comma

            // Extract time
            while (temp[j] != ',') {
                v.time = v.time * 10 + (temp[j] - '0');
                j++;
            }
            j++;  // Skip the comma

            // Extract amount
            while (temp[j] != ',') {
                v.amt = v.amt * 10 + (temp[j] - '0');
                j++;
            }
            j++;  // Skip the comma

            // Extract city
            while (j < m) {
                v.city += temp[j];
                j++;
            }

            v.ind = i;  // Store the index of the transaction
            vec.push_back(v);     
        }

        // First check: If amount >= 1000, it's an invalid transaction
        for (auto& i : vec) {
            if (i.amt >= 1000) {
                invalidIndices.insert(i.ind);  // Mark the transaction as invalid
            }
        }

        // Second check: If same person has transactions in different cities within 60 minutes
        for (int i = 0; i < vec.size(); i++) {
            for (int j = i + 1; j < vec.size(); j++) {  // Avoid redundant comparisons
                if (vec[i].name == vec[j].name && vec[i].city != vec[j].city) {
                    if (abs(vec[i].time - vec[j].time) <= 60) {
                        invalidIndices.insert(vec[i].ind);  // Mark both transactions as invalid
                        invalidIndices.insert(vec[j].ind);
                    }
                }
            }
        }

        // Collect all invalid transactions based on marked indices
        for (auto idx : invalidIndices) {
            ans.push_back(transactions[idx]);
        }

        return ans;
    }
};

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