<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>

import heapq
class Solution:
    def numBusesToDestination(self, routes: List[List[int]], source: int, target: int) -> int:
        if source == target:
            return 0
        n = len(routes)
        adj = [[] for _ in range(n)]
        src_bus = -1
        dest_bus = -1
        for i in range(n):
            for j in range(i):
                inte = set(routes[i]).intersection(set(routes[j]))
                if len(inte):
                    adj[i].append(j)
                    adj[j].append(i)

        for i in range(n):
            if source in routes[i]:
                src_bus = i
            if target in routes[i]:
                dest_bus = i
            if src_bus == dest_bus and src_bus!= -1:
                return 1
        if src_bus == -1 or dest_bus == -1:
            return -1
        for i in range(n):
            adj[i] = list(set(adj[i]))

        pq = [(1,src_bus)]
        vis = [0 for _ in range(n)]
        vis[src_bus] = 1

        while pq:
            change,cur = heapq.heappop(pq)
            if cur == dest_bus:
                return change
            for i in adj[cur]:
                if vis[i]==0:
                    vis[i] = 1
                    heapq.heappush(pq,(change+1,i))

        return -1

        # adj = {}
        # if source == target:
        #     return 0
        # for r in routes:
        #     if source in r and target in r:
        #         return 1
        # r = len(routes)
        # vis_bus = set()
        # for i in range(r):
        #     for j in range(len(routes[i])):
        #         if routes[i][j] not in adj:
        #             adj[routes[i][j]] = []
        #         if j == len(routes[i])-1:
        #             adj[routes[i][j]].append((routes[i][0],i))
        #         else:
        #             adj[routes[i][j]].append((routes[i][j+1],i))
        # pq = [(0,0,-1,source)]
        # vis = [0 for _ in range(max(adj.keys())+1)]
        # mini = 1e9
        # while pq:
        #     stops_,change,bus_no,stop = heapq.heappop(pq)
        #     if stop == target:
        #         mini = min(mini,change)
        #     for i in adj[stop]:
        #         # if i[1] not in vis_bus:
        #             # vis_bus.add(i[1])
        #         if vis[i[0]]==0:
        #             vis[i[0]] = 1
        #             if i[1]!=bus_no:
        #                 heapq.heappush(pq,(stops_+1,change+1,i[1],i[0]))
        #             else:
        #                 heapq.heappush(pq,(stops_+1,change,i[1],i[0]))
        # if mini==1e9:
        #     return -1
        # return mini

            
        
33561