<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>

void dfs(int i, vector<vector<int>>& adjlist, vector<int>& visited, stack<int>& st)
{
    visited[i] = 1;
    for(auto it: adjlist[i])
    {
        if(!visited[it])
        {
            dfs(it,adjlist,visited,st);
        }
    }
    st.push(i);
}

void newdfs(int i, vector<vector<int>>& revadjlist, vector<int>& newvisited, int &maxi, int count)
{
    newvisited[i] = 1;
    maxi = max(maxi,count);
    for(auto it:revadjlist[i])
    {
        if(!newvisited[it])
        {
            count++;
            newdfs(it,revadjlist,newvisited, maxi,count);
        }
    }
}

class Solution {
public:
    int longestCycle(vector<int>& edges) {
        int n = edges.size();
        vector<vector<int>>adjlist(n);

        for(int i=0;i<n;i++)
        {
            if(edges[i]!=-1)
            {
                adjlist[i].push_back(edges[i]);
            }
        }

        vector<int>visited(n+1,0);
        stack<int>st;

        for(int i=0;i<n;i++)
        {
            if(!visited[i])
            {
                dfs(i,adjlist,visited,st);
            }
        }

        vector<vector<int>>revadjlist(n);
        for(int i=0;i<n;i++)
        {
            if(edges[i] != -1)
            {
                revadjlist[edges[i]].push_back(i);
            }
        }

        int maxi = 0;
        vector<int>newvisited(n+1,0);

        while(!st.empty())
        {
            int top = st.top();
            st.pop();

            if(!newvisited[top])
            {
                newdfs(top,revadjlist,newvisited,maxi,0);
            }
        }

        if(maxi == 0) return -1;
        else return maxi+1;
    }
};
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