Leetcode Course Schedule II problem-solving report __topological

Topic

There are a total of n courses your have to take, labeled from 0 to N-1.

Some courses may have prerequisites, for example to take course 0 in have to-a take course 1, which is expressed as a Pair: [0,1]

Given the total number of courses and a list of prerequisite pairs, return the ordering of courses of your should to take SH all courses.

There May is multiple correct orders, you just need to return one of them. If It is impossible to finish all courses, return a empty array.

For example:

2, [[1,0]]

There are a total of 2 courses to take. To take course 1 should have finished course 0. So the correct course order is [0,1]

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

There are a total of 4 courses to take. To take course 3 should have finished both courses 1 and 2. Both Courses 1 and 2 should is taken after you finished course 0. So one correct course the order is [0,1,2,3]. Another correct ordering is[0,2,1,3]. Resolution

Compared to the "Leetcode" Course Schedule problem-solving report, the result returned is a set of sorting results, not whether they can be sorted.

Because as long as the return of any kind of legitimate topology sorting results can only be recorded in the BFS process to access the node.

"Java Code"

public class Solution {public int[] findorder (int numcourses, int[][] prerequisites) {List<set<integer
        >> adjlists = new arraylist<set<integer>> ();
        for (int i = 0; i < numcourses i++) {adjlists.add (New hashset<integer> ()); for (int i = 0; i < prerequisites.length i++) {adjlists.get (prerequisites[i][1]). Add (P
        Rerequisites[i][0]);
        } int[] Indegrees = new int[numcourses];
            for (int i = 0; i < numcourses. i++) {for (int x:adjlists.get (i)) {indegrees[x]++;
        } queue<integer> Queue = new linkedlist<integer> ();
            for (int i = 0; i < numcourses i++) {if (indegrees[i) = = 0) {queue.offer (i);
        } int[] res = new Int[numcourses];
        int count = 0;
            while (!queue.isempty ()) {int cur = queue.poll ();
                for (int x:adjlists.get (cur)) {indegrees[x]--;
                if (indegrees[x] = = 0) {queue.offer (x);
        }} res[count++] = cur;
        } if (count = = numcourses) return res;
    return new int[0]; }
}