leetcode210

public class Solution {
    
    //test case [1,0]
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        int[] map = new int[numCourses];
        int n = prerequisites.length;
        int[] res = new int[numCourses];
        
        for(int i=0; i<n; i++) {
            map[ prerequisites[i][1] ] ++;
        }
        
        Queue<Integer> que = new LinkedList<Integer>();
        int index = numCourses-1;
        for(int i=0; i<numCourses; i++) {
            if(map[i] == 0) {
                que.add(i);
                res[index--] = i;
            }
        }
        
        while(!que.isEmpty() ){
            int k = que.remove();
            for(int i=0; i<n; i++) {
                int l = prerequisites[i][1];
                if(k==prerequisites[i][0]) {
                    map[l]--;
                    if(map[l] == 0) {
                        que.add(l);
                        res[index--] = l;
                    }
                }
            }
        }
        if(index!=-1) return new int[0];
        else return res;
    }
}

补充一个python的实现，使用深度优先遍历，进行拓扑排序：

class Solution:
    def dfs(self,visited,memo,dic,i,postCourse):
        if visited[i]:
            return True
        if memo[i] == 0:
            return False
        elif memo[i] == 1:
            return True
        for cs in dic[i]:
            visited[i] = True
            bl = self.dfs(visited,memo,dic,cs,postCourse)
            visited[i] = False
            if bl:
                memo[i] = 1
                return True
        memo[i] = 0
        postCourse.append(i)
        return False
    def findOrder(self, numCourses: int, prerequisites: 'List[List[int]]') -> 'List[int]':
        dic = {}
        n = len(prerequisites)
        for i in range(numCourses):
            dic[i] = []
        for i in range(n):
            cs = prerequisites[i][0]#当前课程
            pre = prerequisites[i][1]#前置课程
            dic[cs].append(pre)
        visited = [False for _ in range(numCourses)]
        memo = [-1 for _ in range(numCourses)]
        postCourse = []
        for i in range(numCourses):
            if self.dfs(visited,memo,dic,i,postCourse):
                return []
        return postCourse