<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>> &g,vector<bool> &vis,int s, int &res, vector<int > &mem)
    {
        if(s == -1)return ;
        
        
        
        if(vis[s])
        {
            int cnt = -1;
            for(int i=0;i<mem.size();i++)
            {
                
                if(mem[i] == s)
                {
                    cnt = i;
                    break;
                }
                
            }
            
            if(cnt ==-1) return;
            res = max(res,(int)mem.size()-cnt);
            return;
        }
        vis[s] = 1;
        mem.push_back(s);
        for(int i=0;i<g[s].size();i++)
        {
            dfs(g,vis,g[s][i],res,mem);
        }
    }
    
    
    int longestCycle(vector<int>& e) {
        
        int n = e.size();
        vector<vector<int>> g(n);
        for(int i=0;i<n;i++)
        {
            g[i].push_back(e[i]);
        }
        
        vector<bool> vis(n,false);
        
        int res = -1;
        int cnt = 0;
        
        for(int i=0;i<n;i++)
        {
            if(!vis[i])
            {
                vector<int > mem;                
                dfs(g,vis,i,res,mem);
            }
        }
        
        return res;
    }
    
};
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