<p>You are given an array <code>routes</code> representing bus routes where <code>routes[i]</code> is a bus route that the <code>i<sup>th</sup></code> bus repeats forever.</p>

<ul>
	<li>For example, if <code>routes[0] = [1, 5, 7]</code>, this means that the <code>0<sup>th</sup></code> bus travels in the sequence <code>1 -&gt; 5 -&gt; 7 -&gt; 1 -&gt; 5 -&gt; 7 -&gt; 1 -&gt; ...</code> forever.</li>
</ul>

<p>You will start at the bus stop <code>source</code> (You are not on any bus initially), and you want to go to the bus stop <code>target</code>. You can travel between bus stops by buses only.</p>

<p>Return <em>the least number of buses you must take to travel from </em><code>source</code><em> to </em><code>target</code>. Return <code>-1</code> if it is not possible.</p>

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

<pre>
<strong>Input:</strong> routes = [[1,2,7],[3,6,7]], source = 1, target = 6
<strong>Output:</strong> 2
<strong>Explanation:</strong> The best strategy is take the first bus to the bus stop 7, then take the second bus to the bus stop 6.
</pre>

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

<pre>
<strong>Input:</strong> routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12
<strong>Output:</strong> -1
</pre>

<p>&nbsp;</p>

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

<ul>
	<li><code>1 &lt;= routes.length &lt;= 500</code>.</li>
	<li><code>1 &lt;= routes[i].length &lt;= 10<sup>5</sup></code></li>
	<li>All the values of <code>routes[i]</code> are <strong>unique</strong>.</li>
	<li><code>sum(routes[i].length) &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= routes[i][j] &lt; 10<sup>6</sup></code></li>
	<li><code>0 &lt;= source, target &lt; 10<sup>6</sup></code></li>
</ul>

#define PII pair<int, int>
#define PIII pair<int, pair<int, int>>
class Solution {
public:
    int numBusesToDestination(vector<vector<int>>& routes, int source, int target) {
        
        // int 
        if (source == target) return 0;
        vector<int> G[1000003];
        int bus =0;
        queue<PII> q;
        for (auto vec : routes) {
            int sz = vec.size();
            for (int i = 0; i < sz; i++) {
                G[vec[i]].push_back(bus);
            }
            bus++;
        }
        vector<int> vis(1000002, 0);


        for (int i = 0; i < G[source].size(); i++) {
            q.push({G[source][i], 0});
            vis[G[source][i]] = 1;
        }

        
        // source , num of buses // bus no

       while (!q.empty()) {

        PII p = q.front();
        q.pop();
        int busIdx = p.first;
        int numOfBuses = p.second;


        int sz = routes[busIdx].size();

        for (int i = 0; i < sz; i++) {

            if (routes[busIdx][i] == target) return numOfBuses + 1;

            for (int j = 0; j < G[routes[busIdx][i]].size(); j++) {
                int newBus = G[routes[busIdx][i]][j];
                if (!vis[newBus]) {
                    q.push({newBus, numOfBuses+1});
                    vis[newBus] = 1;
                }
            }
        }
       }

       return -1;





    }
};
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