图论32（Leetcode210课程表2）

代码：

class Solution {
    List> edges;
    boolean valid = true;
    int[] visited;
    int[] result;
    int index;
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        edges = new ArrayList<>();
        for(int i=0;i
            edges.add(new ArrayList());
        }
        visited = new int[numCourses];
        result = new int[numCourses];
        index = numCourses - 1;
 
        for(int[] prerequisite:prerequisites){
            edges.get(prerequisite[1]).add(prerequisite[0]);
        }
        for(int i=0;i
            if(visited[i]==0){
                dfs(i);
            }
        }
        if(!valid)return new int[0];
        return result;
    }
    public void dfs(int u){
        visited[u] = 1;
        for(int v:edges.get(u)){
            if(visited[v]==0){
                dfs(v);
                if(!valid)return;
            }else if(visited[v]==1){
                valid = false;
                return;
            }
        }
        visited[u] = 2;
        result[index--] = u;
 
    }
}