added topological sort

TopologicalSort.java

@@ -0,0 +1,83 @@
+import java.lang.*;
+import java.io.*;
+import java.util.*;
+
+class TopologicalSort {
+    public static void main(String[] args) throws IOException {
+        BufferedReader read =
+                new BufferedReader(new InputStreamReader(System.in));
+        int t = Integer.parseInt(read.readLine());
+
+        while (t-- > 0) {
+            ArrayList<ArrayList<Integer>> list = new ArrayList<>();
+            String st[] = read.readLine().trim().split("\\s+");
+            int edg = Integer.parseInt(st[0]);
+            int nov = Integer.parseInt(st[1]);
+
+            for (int i = 0; i < nov + 1; i++)
+                list.add(i, new ArrayList<Integer>());
+
+            String s[] = read.readLine().trim().split("\\s+");
+            int p = 0;
+            for (int i = 1; i <= edg; i++) {
+                int u = Integer.parseInt(s[p++]);
+                int v = Integer.parseInt(s[p++]);
+                list.get(u).add(v);
+            }
+
+            int[] res = new TopologicalSortUtil().topoSort(list, nov);
+
+            if (check(list, nov, res) == true)
+                System.out.println("1");
+            else
+                System.out.println("0");
+        }
+    }
+    static boolean check(ArrayList<ArrayList<Integer>> list, int V, int[] res) {
+        int[] map = new int[V];
+        for (int i = 0; i < V; i++) {
+            map[res[i]] = i;
+        }
+        for (int i = 0; i < V; i++) {
+            for (int v : list.get(i)) {
+                if (map[i] > map[v]) return false;
+            }
+        }
+        return true;
+    }
+}
+
+class TopologicalSortUtil {
+    static int[] topoSort(ArrayList<ArrayList<Integer>> adj, int N) {
+        int[] indegree = new int[N];
+        for(int i=0; i<N; i++) {
+            ArrayList<Integer> temp = adj.get(i);
+            for(int node : temp) {
+                indegree[node]++;
+            }
+        }
+        Queue<Integer> q = new LinkedList<>();
+        for(int i=0; i<N; i++) {
+            if(indegree[i] == 0) {
+                q.add(i);
+            }
+        }
+        int visited = 0;
+        ArrayList<Integer> result = new ArrayList<>();
+        while(!q.isEmpty()) {
+            int u = q.poll();
+            result.add(u);
+            for(int node : adj.get(u)) {
+                if(--indegree[node] == 0) {
+                    q.add(node);
+                }
+            }
+            visited++;
+        }
+        int[] arr = new int[result.size()];
+        for(int i=0; i<result.size(); i++) {
+            arr[i] = result.get(i);
+        }
+        return arr;
+    }
+}