Find Eventual Safe States
<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://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0800-0899/0802.Find%20Eventual%20Safe%20States/images/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>
Depth-First Search; Breadth-First Search; Graph; Topological Sort
class Solution {
    public List<Integer> eventualSafeNodes(int[][] graph) {
        int n = graph.length;
        int[] indeg = new int[n];
        List<Integer>[] rg = new List[n];
        Arrays.setAll(rg, k -> new ArrayList<>());
        Deque<Integer> q = new ArrayDeque<>();
        for (int i = 0; i < n; ++i) {
            for (int j : graph[i]) {
                rg[j].add(i);
            }
            indeg[i] = graph[i].length;
            if (indeg[i] == 0) {
                q.offer(i);
            }
        }
        while (!q.isEmpty()) {
            int i = q.pollFirst();
            for (int j : rg[i]) {
                if (--indeg[j] == 0) {
                    q.offer(j);
                }
            }
        }
        List<Integer> ans = new ArrayList<>();
        for (int i = 0; i < n; ++i) {
            if (indeg[i] == 0) {
                ans.add(i);
            }
        }
        return ans;
    }
}