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Leetcode题目链接

描述⚓︎

详见中文题目链接。

解答⚓︎

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class Solution {
public:
    int minimumSemesters(int n, vector<vector<int>>& relations) {
        vector<vector<int>> edges(n + 1);
        vector<int> inDegree(n + 1, 0);

        for (const auto& info : relations) {
            edges[info[0]].push_back(info[1]);
            inDegree[info[1]]++;
        }

        queue<int> que;
        for (int i = 1; i <= n; i++) {
            if (inDegree[i] == 0)
                que.push(i);
        }

        vector<int> cost(n + 1, 0);
        int res = 0, count = n;
        while (!que.empty()) {
            int current = que.front();
            que.pop();
            count--;

            cost[current]++;
            res = max(res, cost[current]);
            for (int v : edges[current]) {
                cost[v] = max(cost[v], cost[current]);
                if (--inDegree[v] == 0)
                    que.push(v);
            }
        }

        return count == 0 ? res : -1;
    }
};