<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 remove1(int i , set<int> &st , vector<int> &ind ,vector<int> &edges){
        if(st.find(i) != st.end()){
            if(ind[i] == 0){
                st.erase(i);
                if(edges[i] != -1){
                    ind[edges[i]]--;
                    remove1(edges[i] , st , ind , edges);
                }
            }
        }
    }

    

    int longestCycle(vector<int>& edges) {
        int n = edges.size();
        
        vector<int> ind(n , 0);
        vector<int> outd(n , 0);
        set<int> canUse;

        // vector<int> par(n, 0);

        for(int i = 0 ;i < n;i++){
            canUse.insert(i);
            if(edges[i] != -1){
                outd[i]++;
                ind[edges[i]]++;
                // par[edges[i]] = i;
            }
        }

        for(int i = 0 ;i < n;i++){
            remove1(i , canUse , ind , edges);
        }

        int ans = 0;
        vector<int> vis(n , 0);

        for(int i = 0 ;i < n;i++){
            if(!vis[i] && canUse.find(i) != canUse.end()){
                int j = edges[i];
                int cnt = 0;
                while(j != i){
                    vis[j] = 1;
                    j = edges[j];
                    cnt++;
                }
                ans = max(ans , cnt + 1);
            }
        }

        return ans == 0 ? -1 : ans;
    }
};
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