content: import java.util.InputMismatchException;
  import java.util.Scanner;
  import java.util.Stack;
  
  public class TopologicalSort {
      private Stack<Integer> stack;
  
      public TopologicalSort() {
          stack = new Stack<Integer>();
      }
  
      public int[] topological(int adjacency_matrix[][], int source) throws NullPointerException {
          int number_of_nodes = adjacency_matrix[source].length - 1;
          int[] topological_sort = new int[number_of_nodes + 1];
          int pos = 1;
          int j;
          int visited[] = new int[number_of_nodes + 1];
          int element = source;
          int i = source;
          visited[source] = 1;
          stack.push(source);
  
          while (!stack.isEmpty()) {
              element = stack.peek();
              while (i <= number_of_nodes) {
                  if (adjacency_matrix[element][i] == 1 && visited[i] == 1) {
                      if (stack.contains(i)) {
                          System.out.println("TOPOLOGICAL SORT NOT POSSIBLE");
                          return null;
                      }
                  }
                  if (adjacency_matrix[element][i] == 1 && visited[i] == 0) {
                      stack.push(i);
                      visited[i] = 1;
                      element = i;
                      i = 1;
                      continue;
                  }
                  i++;
              }
              j = stack.pop();
              topological_sort[pos++] = j;
              i = ++j;
          }
          return topological_sort;
      }
  
      public static void main(String... arg) {
          int number_no_nodes, source;
          Scanner scanner = null;
          int topological_sort[] = null;
          try {
              System.out.println("Enter the number of nodes in the graph");
              scanner = new Scanner(System.in);
              number_no_nodes = scanner.nextInt();
  
              int adjacency_matrix[][] = new int[number_no_nodes + 1][number_no_nodes + 1];
              System.out.println("Enter the adjacency matrix");
              for (int i = 1; i <= number_no_nodes; i++)
                  for (int j = 1; j <= number_no_nodes; j++)
                      adjacency_matrix[i][j] = scanner.nextInt();
  
              System.out.println("Enter the source for the graph");
              source = scanner.nextInt();
  
              System.out.println("The Topological sort for the graph is given by ");
              TopologicalSort toposort = new TopologicalSort();
              topological_sort = toposort.topological(adjacency_matrix, source);
              System.out.println();
              for (int i = topological_sort.length - 1; i > 0; i--) {
                  if (topological_sort[i] != 0)
                      System.out.print(topological_sort[i] + "\t");
              }
          } catch (InputMismatchException inputMismatch) {
              System.out.println("Wrong Input format");
          } catch (NullPointerException nullPointer) {
          }
          scanner.close();
      }
  }
  