Lintcode: Topological Sorting

Given an directed graph, a topological order of the graph nodes is defined as follow:

For each directed edge A-->B in graph, A must before B in the order list.
The first node in the order can be any node in the graph with no nodes direct to it.
Find any topological order for the given graph.
Note
You can assume that there is at least one topological order in the graph.

Example
For graph as follow: 



The topological order can be:

[0, 1, 2, 3, 4, 5]

or

[0, 2, 3, 1, 5, 4]

or

....



Challenge
Can you do it in both BFS and DFS?

 1 /**
 2  * Definition for Directed graph.
 3  * class DirectedGraphNode {
 4  *     int label;
 5  *     ArrayList<DirectedGraphNode> neighbors;
 6  *     DirectedGraphNode(int x) { label = x; neighbors = new ArrayList<DirectedGraphNode>(); }
 7  * };
 8  */
 9 public class Solution {
10     /**
11      * @param graph: A list of Directed graph node
12      * @return: Any topological order for the given graph.
13      */    
14     public ArrayList<DirectedGraphNode> topSort(ArrayList<DirectedGraphNode> graph) {
15         // write your code here
16         ArrayList<DirectedGraphNode> res = new ArrayList<DirectedGraphNode>();
17         if (graph.size() == 0) return res;
18         HashMap<DirectedGraphNode, Set<DirectedGraphNode>> map = new HashMap<DirectedGraphNode, Set<DirectedGraphNode>>();
19         for (DirectedGraphNode each : graph) {
20             map.put(each, new HashSet<DirectedGraphNode>());
21         }
22         for (DirectedGraphNode each : graph) {
23             for (int i=0; i<each.neighbors.size(); i++) {
24                 map.get(each.neighbors.get(i)).add(each);
25             }
26         }
27         while (graph.size() > 0) {
28             int index = 0;
29             while (index < graph.size()) {
30                 DirectedGraphNode cur = graph.get(index);
31                 if (map.get(cur).size() == 0) {
32                     //add the node to our result
33                     //remove the node from the graph
34                     res.add(cur);
35                     graph.remove(index);
36                     for (DirectedGraphNode elem : graph) {
37                         if (map.get(elem).contains(cur)) {
38                             map.get(elem).remove(cur);
39                         }
40                     }
41                 }
42                 else index++;
43             }
44         }
45         return res;
46     }
47 }

 1 /**
 2  * Definition for Directed graph.
 3  * class DirectedGraphNode {
 4  *     int label;
 5  *     ArrayList<DirectedGraphNode> neighbors;
 6  *     DirectedGraphNode(int x) { label = x; neighbors = new ArrayList<DirectedGraphNode>(); }
 7  * };
 8  */
 9 public class Solution {
10     /**
11      * @param graph: A list of Directed graph node
12      * @return: Any topological order for the given graph.
13      */    
14     public ArrayList<DirectedGraphNode> topSort(ArrayList<DirectedGraphNode> graph) {
15         // write your code here
16         ArrayList<DirectedGraphNode> res= new ArrayList<DirectedGraphNode>();
17         if (graph.size() == 0) return res;
18         HashMap<DirectedGraphNode, Integer> status = new HashMap<DirectedGraphNode, Integer>();
19         for (DirectedGraphNode elem : graph) {
20             status.put(elem, 0);
21         }
22         ArrayList<DirectedGraphNode> templist = new ArrayList<DirectedGraphNode>();
23         templist.add(null);
24         while (hasUnvisited(graph, status, templist)) {
25             DirectedGraphNode cur = templist.get(0);
26             templist.set(0, null);
27             search(cur, status, res);
28         }
29         return res;
30     }
31     
32     public boolean hasUnvisited(ArrayList<DirectedGraphNode> graph, HashMap<DirectedGraphNode, Integer> status, ArrayList<DirectedGraphNode> templist) {
33         for (DirectedGraphNode elem : graph) {
34             if (status.get(elem) == 0) {
35                 templist.set(0, elem);
36                 return true;
37             }
38         }
39         return false;
40     }
41     
42     public void search(DirectedGraphNode cur, HashMap<DirectedGraphNode, Integer> status, ArrayList<DirectedGraphNode> res) {
43         if (status.get(cur) == 1) System.out.println("not a DAG");
44         if (status.get(cur) == 2) return;
45         status.put(cur, 1);
46         for (DirectedGraphNode neigh : cur.neighbors) {
47             search(neigh, status, res);
48         }
49         status.put(cur, 2);
50         res.add(0, cur);
51     }
52 }