Topological Sor-207. Course Schedule

There are a total of n courses you have to take, labeled from 0 to n - 1.

Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]

Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?

For example:

2, [[1,0]]

There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.

2, [[1,0],[0,1]]

There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.

Note:

The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.
You may assume that there are no duplicate edges in the input prerequisites.

class Solution {

public:

    bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) {

        vector<vector<int>> graph(numCourses, vector<int>());

        vector<int> in(numCourses, );

        for (auto a : prerequisites) {

            graph[a.second].push_back(a.first);

            ++in[a.first];

        }

        queue<int> q;

        for (int i = ; i < numCourses; ++i) {

            if (in[i] == ) q.push(i);

        }

        while (!q.empty()) {

            int t = q.front();

            q.pop();

            for (auto a : graph[t]) {

                --in[a];

                if (in[a] == ) q.push(a);

            }

        }

        for (int i = ; i < numCourses; ++i) {

            if (in[i] != ) return false;

        }

        return true;

    }

};

巴特西

Topological Sor-207. Course Schedule

最新文章

热门文章