Topological Sorting

Topological Sorting

题目地址

https://www.lintcode.com/problem/topological-sorting/description

题目描述

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.

代码

class Graph {
  private int V;
  private LinkedList<Integer> adj[];

  Graph(int v) {
    V = v;
    adj = new LinkedList[v];
    for (int i = 0; i < v; i++) {
      adj[i] = new LinkedList();
    }

    void addEdge(int v, int w) { adj[v].add(w); }

    void topologicalSortUtil(int v, boolean visited[], Stack stack) {
      visited[v] = true;
      Integer i;

      Iterator<Integer> it = adj[v].iterator();
      while (it.hasNext()) {
        i = it.next();
        if (!visited[i]) {
          topologicalSortUtil(i, visited, stack);
        }
      }

      stack.push(new Integer(v));
    }

    void topologicalSort() {
      Stack stack = new Stack();

      boolean visited[] = new boolean[V];
      for (int i = 0; i < V; i++) {
        visited[i] = false;
      }

      for (int i = 0; i < V; i++) {
        if (visited[i] == false) {
          topologicalSortUtil(i, visited, stack);
        }
      }

      while (stack.empty() == false) {
        System.out.print(stack.pop() + " ");
      }

    }

  }
}