<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:
    bool dfs(int node,vector<vector<int>>& adj,vector<bool>& vis,vector<int>& parent,int start,int &len){
        
        vis[node] = 1;
        for(auto nbr : adj[node]) { 
            if(!vis[nbr]) { 
                parent[nbr] = node;
                bool foundcycle = dfs(nbr,adj,vis,parent,start,len);
                if(foundcycle) return true;
            }else if(nbr == start) { 
                len = 1;
                for(int nodes = node ; nodes != start ; nodes = parent[nodes] ){ 
                    len ++;
                }
                return true;
            }
        }
       
        return false;
    }
    int longestCycle(vector<int>& edges) {
        int n = edges.size();
        vector<int>indeg(n,0);
        
        vector<vector<int>>adj(n);
        for(int i = 0 ; i < n ; i ++ ){ 
            if(edges[i] != -1){ 
                indeg[edges[i]] ++;
                adj[i].push_back(edges[i]);
            }
        }

        queue<int>q;
        for(int i = 0 ; i < n ; i ++ ) { 
            if(indeg[i] == 0){ 
                q.push(i);
            }
        }      
        int cnt = 0;
        while(!q.empty()){ 
            int top = q.front();
            q.pop();
            cnt ++;
            for(int nbr : adj[top])  {             
                indeg[nbr] --;
                if(indeg[nbr] == 0){ 
                    q.push(nbr);
                }
            }
        }

        int maxi = -1;
        if(cnt != n) { 
            vector<bool>vis(n,false);
            vector<int>parent(n,-1);
            for(int i = 0 ; i < n ; i ++ ){ 
                if(indeg[i] != 0 && !vis[i]){ 
                    int len = 0;
                    if(dfs(i,adj,vis,parent,i,len)) { 
                        maxi = max(maxi,len);
                    }

                }
            }
        }

        return maxi;
    }
};
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