<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:
    static bool DFS(vector<vector<int>> &adj , vector<bool> &vis  , vector<bool> &rec ,int o,int &count){
        vis[o] = true;rec[o] = true;

        for(auto it : adj[o]){
            if(vis[it] == false  ){
                if (DFS(adj , vis , rec, it,count)){
                    rec[o]=false;
                    return true;  
                }
                 
            }
            else if(rec[it] == true){
                int curr=0;
                curr = adj[it][0]; 
                rec[o]=false;
                while(curr!=it){
                    count++;
                    curr = adj[curr][0];
                    rec[curr]=false;
                }
                
                count++;
                return  true;
            }
            rec[it]=false;
        }
        rec[o]=false;
        return false;
    }


    int longestCycle(vector<int>& v) {
        int n = v.size() ;
        int ans = 0;
        bool isCycle = false;
        
        
        vector<vector<int>> adj(n);
        vector<bool>  vis(n , false);
        vector<bool>  rec(n , false);
        for(int i = 0 ; i< n ;i++){
           if(v[i]!=-1) adj[i].push_back(v[i]);
        }
    

        for(int i = 0 ; i<n ; i++){
            if(vis[i] == false){
               
                int count = 0;
                DFS(adj ,vis , rec, i,count );
                if(count>0) isCycle = true;
                ans=max(ans, count);
            }
        }
        if(!isCycle) return -1;
        return ans;
        
    }
};
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