From 6ed7a6f8d83d622e95825ad5d33359235d9b801d Mon Sep 17 00:00:00 2001
From: Dhruvi Agrawal <60813752+dhruviagrawal@users.noreply.github.com>
Date: Sat, 2 Oct 2021 18:38:57 +0530
Subject: [PATCH] Topological Sort-BFS-graphs

---
 Algorithms/TopologicalSort.cpp | 79 ++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 Algorithms/TopologicalSort.cpp

diff --git a/Algorithms/TopologicalSort.cpp b/Algorithms/TopologicalSort.cpp
new file mode 100644
index 0000000..88c34c4
--- /dev/null
+++ b/Algorithms/TopologicalSort.cpp
@@ -0,0 +1,79 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+//Using BFS Algorithm
+//Intuition- indegree zero nodes wont have any edges so they are placed before. 
+//indegree is being reduced as zero indegree nodes where taken beforehand.
+
+class Solution
+{
+	public:
+	//Function to return list containing vertices in Topological order. 
+	//BFS Algo is used
+	vector<int> topoSort(int V, vector<int> adj[]) 
+	{
+	    queue<int>q;
+	    vector<int>indegree(V,0);
+	    for(int i=0;i<V;i++)
+	    {
+	        for(auto it:adj[i])
+	        indegree[it]++;
+	    }
+	    for(int i=0;i<V;i++)
+	    {
+	        if(indegree[i]==0)
+	        q.push(i);
+	    }
+	    vector<int>topo;
+	    while(!q.empty())
+	    {
+	        int node=q.front();
+	        q.pop();
+	        topo.push_back(node);
+	        for(auto it:adj[node])
+	        {
+	            indegree[it]--;
+	            if(indegree[it]==0)
+	            q.push(it);
+	        }
+	    }
+	    return topo;
+	}
+};
+
+int check(int V, vector <int> &res, vector<int> adj[]) {
+    vector<int> map(V, -1);
+    for (int i = 0; i < V; i++) {
+        map[res[i]] = i;
+    }
+    for (int i = 0; i < V; i++) {
+        for (int v : adj[i]) {
+            if (map[i] > map[v]) return 0;
+        }
+    }
+    return 1;
+}
+
+int main() {
+    int T;
+    cin >> T;
+    while (T--) {
+        int N, E;
+        cin >> E >> N;
+        int u, v;
+
+        vector<int> adj[N];
+
+        for (int i = 0; i < E; i++) {
+            cin >> u >> v;
+            adj[u].push_back(v);
+        }
+        
+        Solution obj;
+        vector <int> res = obj.topoSort(N, adj);
+
+        cout << check(N, res, adj) << endl;
+    }
+    
+    return 0;
+}