longest-cycle-in-a-graph

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Algorithms

You are given a directed graph of <code>n</code> nodes numbered from <code>0</code> to <code>n - 1</code>, where each node has at most one outgoing edge.

The graph is represented with a given 0-indexed 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>.

Return the length of the longest cycle in the graph. If no cycle exists, return <code>-1</code>.

A cycle is a path that starts and ends at the same node.

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2022/06/08/graph4drawio-5.png" style="width: 335px; height: 191px;" />
<pre>
Input: edges = [3,3,4,2,3]
Output: 3
Explanation: 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>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2022/06/07/graph4drawio-1.png" style="width: 171px; height: 161px;" />
<pre>
Input: edges = [2,-1,3,1]
Output: -1
Explanation: There are no cycles in this graph.
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>n == edges.length</code></li>
	<li><code>2 &lt;= n &lt;= 105</code></li>
	<li><code>-1 &lt;= edges[i] &lt; n</code></li>
	<li><code>edges[i] != i</code></li>
</ul>