<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 f(int i, unordered_map<int,vector<int>>&mpp, vector<bool>&v1, int &cnt){
    //     int total=1;
    //     v1[i]=1;
    //     for(auto vec:mpp[i]){
    //         if(!v1[vec]){
    //             f(vec,mpp,v1,cnt);
    //             total+=cnt;
    //         }
    //     }

    //     cnt=total;
    // }
    int f(int node, unordered_map<int,int>&mpp, vector<bool>&vis, vector<bool>&st, vector<int>&dis){
        vis[node] = 1;
        st[node] = 1;
        int len=-1;

        if(mpp.find(node)!=mpp.end()){
            int adjnode=mpp[node];
            if(!vis[adjnode]){
                dis[adjnode]=1+dis[node];
                len=f(adjnode,mpp,vis,st,dis);
            }
            else if(st[adjnode]){
                len=dis[node]-dis[adjnode]+1;
            }
        }
        st[node] = 0;
        return len;
    }

    int longestCycle(vector<int>& edges) {
        int n = edges.size();
        unordered_map<int, int>mpp;
        for (int i=0;i<n;i++){
            if (edges[i] ==-1) continue;
            mpp[i]=edges[i];
        }
        vector<bool>vis(n,0);
        vector<bool>st(n,0);
        vector<int>dis(n,0);
        int maxi=INT_MIN;
        for (int i=0;i<n;i++){
            if(!vis[i]){
                int cnt=f(i,mpp,vis,st,dis);
                maxi=max(maxi,cnt);
            }
        }
        if(maxi==INT_MIN) return -1;
        return maxi;
    }
};
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