leetcode-problemset/leetcode/problem/find-eventual-safe-states.html

<p>There is a directed graph of <code>n</code> nodes with each node labeled from <code>0</code> to <code>n - 1</code>. The graph is represented by a <strong>0-indexed</strong> 2D integer array <code>graph</code> where <code>graph[i]</code> is an integer array of nodes adjacent to node <code>i</code>, meaning there is an edge from node <code>i</code> to each node in <code>graph[i]</code>.</p>

<p>A node is a <strong>terminal node</strong> if there are no outgoing edges. A node is a <strong>safe node</strong> if every possible path starting from that node leads to a <strong>terminal node</strong> (or another safe node).</p>

<p>Return <em>an array containing all the <strong>safe nodes</strong> of the graph</em>. The answer should be sorted in <strong>ascending</strong> order.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="Illustration of graph" src="https://s3-lc-upload.s3.amazonaws.com/uploads/2018/03/17/picture1.png" style="height: 171px; width: 600px;" />
<pre>
<strong>Input:</strong> graph = [[1,2],[2,3],[5],[0],[5],[],[]]
<strong>Output:</strong> [2,4,5,6]
<strong>Explanation:</strong> The given graph is shown above.
Nodes 5 and 6 are terminal nodes as there are no outgoing edges from either of them.
Every path starting at nodes 2, 4, 5, and 6 all lead to either node 5 or 6.</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> graph = [[1,2,3,4],[1,2],[3,4],[0,4],[]]
<strong>Output:</strong> [4]
<strong>Explanation:</strong>
Only node 4 is a terminal node, and every path starting at node 4 leads to node 4.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == graph.length</code></li>
	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= graph[i].length &lt;= n</code></li>
	<li><code>0 &lt;= graph[i][j] &lt;= n - 1</code></li>
	<li><code>graph[i]</code> is sorted in a strictly increasing order.</li>
	<li>The graph may contain self-loops.</li>
	<li>The number of edges in the graph will be in the range <code>[1, 4 * 10<sup>4</sup>]</code>.</li>
</ul>