Merge pull request larissalages#180 from ErR0rpj/master

Topological Sort (Graphs)

Author: larissalages

classical_algorithms/c++/Topological_sort.cpp

@@ -0,0 +1,72 @@
+//Topological Sorting of directed and acyclic graph.
+//It is done by BFS and using in_degree array. 
+//It has one property that it returns the sorting in lexographical order.
+#include<bits/stdc++.h>
+using namespace std;
+
+int vertices,edges;
+vector<int>adjcency_list[100001];
+
+vector<int> topological_sort(){
+    vector<int> topo;
+    int in_degree[vertices+1];
+    bool visited[vertices+1];
+    priority_queue<int,vector<int>,greater<int>> q;
+
+    for(int i=1;i<=vertices;i++){
+        visited[i]=false;
+        in_degree[i]=0;
+    }
+
+    for(int i=1;i<=vertices;i++){
+        for(int j:adjcency_list[i]){
+            in_degree[j]=in_degree[j]+1;
+        }
+    }
+
+    for(int i=1;i<=vertices;i++){
+        if(in_degree[i]==0){
+            visited[i]=true;
+            q.push(i);
+        }
+    }
+    int k=0;
+    while(!q.empty()){
+        int v=q.top();
+        q.pop();
+        topo.push_back(v);
+        for(int i:adjcency_list[v]){
+            if(visited[i]==false){
+                in_degree[i]=in_degree[i]-1;
+                if(in_degree[i]==0){
+                    q.push(i);
+                    visited[i]=true;
+                }
+            }
+        }
+    }
+    return topo;
+}
+
+int main(){
+    cout<<"Enter number of vertices and edges:\n";
+    cin>>vertices>>edges;
+
+    vector<int> topological_sorted;
+    
+    cout<<"Enter the edges directed from X (first number) to Y (second number):\n";
+    for(int i=0;i<edges;i++){
+        int u,v;
+        cin>>u>>v;
+        adjcency_list[u].push_back(v);
+    }
+
+    topological_sorted=topological_sort();
+
+    cout<<"Topological Sort of the given graph: ";
+    for(int i=0;i<topological_sorted.size();i++){
+        cout<<topological_sorted[i]<<" ";
+    }
+    cout<<"\n";
+    return 0;
+}

readme.md

@@ -43,6 +43,7 @@ Code | Test
 [Quick Sort](https://github.com/kartikeysingh6/code_problems/blob/master/classical_algorithms/c++/quicksort.cpp) | Missing tests
 [0/1 Knapsack Problem](https://github.com/ErR0rpj/code_problems/blob/master/classical_algorithms/c%2B%2B/01_knapsack_problem.cpp) | Missing tests
 [Kadane's Algorithm](https://github.com/ErR0rpj/code_problems/blob/master/classical_algorithms/c%2B%2B/Kadane_Algorithm.cpp) | Missing tests
+[Topological Sort](https://github.com/ErR0rpj/code_problems/blob/master/classical_algorithms/c%2B%2B/Topological_sort.cpp) | Missing Tests
 
 # Codeforces