题解 | #牛群的喂养顺序II#

class Solution {
public:
    /**
     * 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vector<vector<>> 
     * @return int整型vector
     */
    vector<int> findFeedOrderII(int numCows, vector<vector<int> >& feedOrders) {
        // write code here
        vector<vector<int>> adjenct(numCows);
        vector<int> ans;
        vector<int> indegree(numCows);
        queue<int> q;
        for (auto& feedOrder : feedOrders) {
            adjenct[feedOrder[1]].push_back(feedOrder[0]);
            indegree[feedOrder[0]]++;
        }
        for (int i = 0; i < numCows; i++) {
            if (indegree[i] == 0) {
                q.push(i);
            }
        }
        while (q.size()) {
            int cow = q.front();
            q.pop();
            numCows--;
            ans.push_back(cow);
            for (auto& nextcow : adjenct[cow]) {
                if (--indegree[nextcow] == 0) {
                    q.push(nextcow);
                }
            }
        }
        if (!numCows) return ans;
        return {};
    }
};