题解 | 牛群的喂养顺序

1. 典型拓扑
2. 注意入度和建图即可。

import java.util.*;


public class Solution {
    public boolean canFeedAllCows (int numCows, int[][] feedOrders) {
        int[] inDegree = new int[numCows];
        boolean[][] graph = new boolean[numCows][numCows];
        for (int i = 0; i < feedOrders.length; ++i) {
            ++inDegree[feedOrders[i][0]];
            graph[feedOrders[i][1]][feedOrders[i][0]] = true;
        }

        Deque<Integer> q = new ArrayDeque<>();
        for (int i = 0; i < numCows; ++i) {
            if (inDegree[i] == 0) {
                q.addLast(i);
            }
        }

        int visitedCnt = 0;
        while (!q.isEmpty()) {
            final int u = q.removeFirst();
            visitedCnt++;
            for (int v = 0; v < numCows; ++v) {
                if (graph[u][v]) {
                    if (--inDegree[v] == 0) {
                        q.addLast(v);
                    }
                }
            }
        }

        return visitedCnt == numCows;
    }
}