<p>There are a total of <code>numCourses</code> courses you have to take, labeled from <code>0</code> to <code>numCourses - 1</code>. You are given an array <code>prerequisites</code> where <code>prerequisites[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> indicates that you <strong>must</strong> take course <code>b<sub>i</sub></code> first if you want to take course <code>a<sub>i</sub></code>.</p>

<ul>
	<li>For example, the pair <code>[0, 1]</code>, indicates that to take course <code>0</code> you have to first take course <code>1</code>.</li>
</ul>

<p>Return <code>true</code> if you can finish all courses. Otherwise, return <code>false</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0]]
<strong>Output:</strong> true
<strong>Explanation:</strong> There are a total of 2 courses to take. 
To take course 1 you should have finished course 0. So it is possible.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0],[0,1]]
<strong>Output:</strong> false
<strong>Explanation:</strong> 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.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= numCourses &lt;= 2000</code></li>
	<li><code>0 &lt;= prerequisites.length &lt;= 5000</code></li>
	<li><code>prerequisites[i].length == 2</code></li>
	<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub> &lt; numCourses</code></li>
	<li>All the pairs prerequisites[i] are <strong>unique</strong>.</li>
</ul>

class Solution {
public:
    void dfs(vector<vector<int>> &graph,int src,vector<int> &indegree )
    {
          for(auto it:graph[src])
          {
               if(--indegree[it]==0)
               dfs(graph,it,indegree);
          } 
    }
    bool canFinish(int n, vector<vector<int>>& p) {
        if(n==1 || p.size()==0 || p.size()==1)
        return true;
        vector<vector<int>> graph(n);
        vector<int> indegree(n,0);
        for(int i=0;i<p.size();i++)
        {
            graph[p[i][1]].push_back(p[i][0]);
            indegree[p[i][0]]++;
        }
        vector<int> temp;
        for(int i=0;i<n;i++)
        {
             if(indegree[i]==0)
             {
                temp.push_back(i);
             }
        }
       for(auto i:temp)
       {
            dfs(graph,i,indegree);
    
       }
       for(auto it:indegree)
       {
          if(it>0)
         return false;
       }
       return true;
    }
};
17000