day51.cpp

#include <iostream>
#include <vector>
#include <queue>
using namespace std;
class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
    vector<vector<int>>graph(numCourses);
    vector<int>indegree(numCourses,0);
    for (auto& p:prerequisites){
        graph[p[1]].push_back(p[0]);
        indegree[p[0]]++;
    }
    queue<int>q;
    for (int i=0;i<numCourses;++i){
        if (indegree[i]==0){
            q.push(i);
        }
    }
    int visited=0;
    while (!q.empty()){
        int course=q.front();
        q.pop();
        visited++;
        for (int next:graph[course]){
            indegree[next]--;
            if (indegree[next]==0){
                q.push(next);
            }
        }
    }
    return visited ==numCourses;
    }
};