题解 | #牛群的喂养顺序#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param numCows int整型
     * @param feedOrders int整型二维数组
     * @return bool布尔型
     */
    public boolean canFeedAllCows (int numCows, int[][] feedOrders) {
        // write code here
        int[] feed = new int[numCows];
        int visited = 0;
        Queue<Integer> queue = new ArrayDeque<>();
        List<List<Integer>> lists = new ArrayList<>();
        for (int i = 0; i < numCows; i++) {
            lists.add(new ArrayList<>());
        }
        for (int[] feedOrder : feedOrders) {
            feed[feedOrder[0]]++;
            lists.get(feedOrder[1]).add(feedOrder[0]);
        }
        for (int i = 0; i < numCows; i++) {
            if (feed[i] == 0) {
                queue.offer(i);
                visited++;
            }
        }
        while (!queue.isEmpty()) {
            int index = queue.poll();
            List<Integer> list = lists.get(index);
            for (int i : list) {
                feed[i]--;
                if (feed[i] == 0) {
                    queue.offer(i);
                    visited++;
                }
            }
        }
        return visited == numCows;
    }
}