<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>

class Solution {
public:
    int numBusesToDestination(vector<vector<int>>& r, int s, int t) {
        set<int>v[r.size()];
        int d[r.size()];
        memset(d,0x1,sizeof(d));
        for(int i=0;i<r.size();i++){
            for(int u:r[i]){
                v[i].insert(u);
            }
        }
        queue<int>q;
        if(s==t){
            return 0;
        }
        for(int i=0;i<r.size();i++){
            if(v[i].count(s)){
                if(v[i].count(t)){
                    return 1;
                }
               // cout<<i<<" ";
                q.push(i);
                d[i]=1;
            }
        }
        int ans=1e9;
        while(q.size()){
            int l=q.front();
            q.pop();
            for(int i=0;i<r.size();i++){
                if(i==l)continue;
                int f=0;
                for(int x:v[l]){
                    if(v[i].count(x)){
                        f=1;
                        break;
                    }
                }
                if(f&&d[i]>d[l]+1){
                    if(v[i].count(t)){
                        ans=min(ans,d[l]+1);
                    }
                    else{
                        d[i]=d[l]+1;
                        q.push(i);
                    }
                }
            }
        }
        if(ans==1e9)return -1; 
        return ans;
    }
};
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