LeetCode 207. Course Schedule(拓扑排序)

class Solution {
public:
    
    vector<int> edge[10005];
    int a[10005];
    int b[10005];
    int vis[10005];
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
        
        if(numCourses==0||numCourses==1)
            return true;
        
        if(prerequisites.size()==0)
            return true;
        
        for(int i=0;i<prerequisites.size();i++)
        {
            edge[prerequisites[i][1]].push_back(prerequisites[i][0]);
            a[prerequisites[i][0]]++;
            b[prerequisites[i][1]]++;
        }
        
        int num=0;
        while(1)
        {
            int tag=0;
            for(int i=0;i<numCourses;i++)
            {
                if(vis[i]==1)
                    continue;
                if(a[i]!=0)
                    continue;
                
                for(int j=0;j<edge[i].size();j++)
                {
                    a[edge[i][j]]--;
                }
                
                num++;
                tag=1;
                    
                vis[i]=1;
            }
            if(tag==0)
                break;
        }
        
        if(num != numCourses)
            return false;
        return true;
        
    }
};