<p>You are given a <strong>directed</strong> graph of <code>n</code> nodes numbered from <code>0</code> to <code>n - 1</code>, where each node has <strong>at most one</strong> outgoing edge.</p>

<p>The graph is represented with a given <strong>0-indexed</strong> array <code>edges</code> of size <code>n</code>, indicating that there is a directed edge from node <code>i</code> to node <code>edges[i]</code>. If there is no outgoing edge from node <code>i</code>, then <code>edges[i] == -1</code>.</p>

<p>Return <em>the length of the <strong>longest</strong> cycle in the graph</em>. If no cycle exists, return <code>-1</code>.</p>

<p>A cycle is a path that starts and ends at the <strong>same</strong> node.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/06/08/graph4drawio-5.png" style="width: 335px; height: 191px;" />
<pre>
<strong>Input:</strong> edges = [3,3,4,2,3]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The longest cycle in the graph is the cycle: 2 -&gt; 4 -&gt; 3 -&gt; 2.
The length of this cycle is 3, so 3 is returned.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/06/07/graph4drawio-1.png" style="width: 171px; height: 161px;" />
<pre>
<strong>Input:</strong> edges = [2,-1,3,1]
<strong>Output:</strong> -1
<strong>Explanation:</strong> There are no cycles in this graph.
</pre>

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

<ul>
	<li><code>n == edges.length</code></li>
	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>-1 &lt;= edges[i] &lt; n</code></li>
	<li><code>edges[i] != i</code></li>
</ul>

class Solution {
public:
    void dfs(vector<vector<int>> &adj,vector<bool> &vis,int &cnt,int sv){
        vis[sv]=true;
        cnt++;
        for(auto it:adj[sv]){
            if(!vis[it]){
                dfs(adj,vis,cnt,it);
            }
        }
    }

    int longestCycle(vector<int>& edges) {
        int n=edges.size();
        vector<vector<int>> adj(n);
        vector<int> indegree(n,0);
        for(int i=0;i<edges.size();i++){
            if(edges[i]==-1) continue;
            adj[i].push_back(edges[i]);
            indegree[edges[i]]++;
        }
        queue<int> q;
        set<int> st;
        for(int i=0;i<n;i++){
            if(indegree[i]==0){
                q.push(i);
            }
        }
        
        //cout<<q.size()<<endl;
        while(!q.empty()){
            int node=q.front();
            q.pop();
            st.insert(node);
            for(auto it:adj[node]){
                indegree[it]--;
                if(indegree[it]==0) q.push(it);
            }
        }
       // cout<<st.size()<<endl;
        vector<int> v;
        vector<bool> vis(n,false);
        for(int i=0;i<n;i++){
            if(st.find(i)!=st.end()){
                vis[i]=true;
            }
            else{
                v.push_back(i);
            }
        }
        int maxi=-1;
        //cout<<v.size();
        for(int i=0;i<v.size();i++){
            int cnt=0;
            if(!vis[v[i]]) dfs(adj,vis,cnt,v[i]);
            maxi=max(maxi,cnt);
        }
        return maxi;

    }
};
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