<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 {
int n;
int ans;
vector<vector<int>> gr;
public:
    void init(int nodes){
        ans =-1;
        n = nodes;
        gr.resize(n+1);
        return;
    }
public:     
    void dfs(int node, vector<bool>& vis, vector<bool>& path, stack<int>& s){

        vis[node] = 1;
        path[node] = 1;
        int f = -1;
        s.push(node);
        for(int& v: gr[node]){
            if(!vis[v])
                dfs(v, vis, path , s);
            else if(vis[v] && path[v]){
                f = v;
                break;
                // while()
            }
        }
        if(f != -1){
            stack<int> temp = s;
            int top = temp.top();
            int cnt = 1;
            while(temp.top() != f){
                temp.pop();
                cnt++;
            }
             
            ans = max(ans, cnt);
            // return;
        }
        s.pop();
        path[node] = 0;
        return;

    }
public:
    int longestCycle(vector<int>& edges) {
        init(edges.size());
        for(int i = 0; i < n; i++){
            if(edges[i] != -1)
            gr[i].push_back(edges[i]);
        }
        vector<bool> vis(n, 0);
        stack<int> cycle;
        vector<bool> path(n, 0);
        for(int i = 0; i < n; i++){
            if(!vis[i]){
                // stack<int> cycle;
                dfs(i, vis, path, cycle);
            }
        }

        return ans;
        
    }
};
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