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2192-all-ancestors-of-a-node-in-a-directed-acyclic-graph/2192-all-ancestors-of-a-node-in-a-directed-acyclic-graph.java

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+import java.util.*;
+class Solution {
+    public static ArrayList<Integer> bfs(ArrayList<ArrayList<Integer>> adjList, int start) {
+        Queue<Integer> queue = new ArrayDeque<>();
+        ArrayList<Integer> ans = new ArrayList<>();
+        // 메모리 초과 나면, ArrayList에 넣어서 sort 하는걸로 시도
+        TreeSet<Integer> set = new TreeSet<>();
+        queue.offer(start);
+        set.add(start);
+        while (!queue.isEmpty()) {
+            int target = queue.poll();
+            for (int elem : adjList.get(target)) {
+                if (!set.contains(elem)) {
+                    set.add(elem);
+                    queue.offer(elem);
+                }
+            }
+        }
+        for (int elem : set) {
+            if (elem != start) {
+                ans.add(elem);
+            }
+        }
+        return ans;
+    }
+    public List<List<Integer>> getAncestors(int n, int[][] edges) {
+        ArrayList<ArrayList<Integer>> adjList = new ArrayList<>();
+        List<List<Integer>> answer = new ArrayList<>();
+        for (int i = 0; i < n; i++) {
+            adjList.add(new ArrayList<>());
+        }
+        for (int[] edge : edges) {
+            int start = edge[0];
+            int end = edge[1];
+            adjList.get(end).add(start);
+        }
+        for (int i = 0; i < n; i++) {
+            answer.add(bfs(adjList, i));
+        }
+        return answer;
+    }
+}