From 05fbe8483f52bc11796e24112971bd77664bb0ff Mon Sep 17 00:00:00 2001
From: Disha167 <khattridisha14@gmail.com>
Date: Tue, 20 Oct 2020 03:19:28 +0530
Subject: [PATCH] Create topological sort.cpp

---
 CPP/graphs/topological sort.cpp | 88 +++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 CPP/graphs/topological sort.cpp

diff --git a/CPP/graphs/topological sort.cpp b/CPP/graphs/topological sort.cpp
new file mode 100644
index 0000000..0d77e8d
--- /dev/null
+++ b/CPP/graphs/topological sort.cpp	
@@ -0,0 +1,88 @@
+//This sort algorithm is used to find dependency among files . Below is its simple to understand implementation using bfs
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int *topoSort(int N, vector<int> adj[]);
+
+/*  Function to check if elements returned by user
+*   contains the elements in topological sorted form
+*   V: number of vertices
+*   *res: array containing elements in topological sorted form
+*   adj[]: graph input
+*/
+bool check(int V, 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 false;
+        }
+    }
+    return true;
+}
+
+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);
+        }
+
+        int *res = topoSort(N, adj);
+
+        cout << check(N, res, adj) << endl;
+    }
+
+// The Graph structure is as folows
+
+/*  Function which sorts the graph vertices in topological form
+*   N: number of vertices
+*   adj[]: input graph
+*   NOTE: You must return dynamically allocated array
+*/
+int* topoSort(int V, vector<int> adj[]) {
+    int indegree[V]={0};
+    int index=0;
+    int *result=new int[V];
+    for(int i=0;i<V;i++)
+    {
+        for(int x:adj[i])
+        {
+            indegree[x]++;
+        }
+    }
+    queue<int>q;
+    for(int i=0;i<V;i++)
+    {
+        if(indegree[i]==0)
+            q.push(i);
+    }
+    while(!q.empty())
+    {
+        int t=q.front();
+        q.pop();
+        result[index++]=t;
+        for(int x:adj[t])
+        {
+            indegree[x]--;
+            if(indegree[x]==0)
+            {
+                q.push(x); 
+                
+            }
+        }
+    }
+    return result;
+   
+}