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kahn's algorithm.cpp
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kahn's algorithm.cpp
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//Kahn’s Algorithm for Topological Sort
//Kahn’s algorithm in order to form topological order constantly looks for the vertices that have no incoming edge and removes all outgoing edges from them.
//Basically, the algorithm:
//1.Finds the vertex that has no incoming edges.
//2.Remove all outgoing edges from that vertex.
//3.Add vertex to the topological order.
//4.Repeat the process until all the vertices are processed.
#include <bits/stdc++.h>
using namespace std;
vector <int> topoSort(vector<int>adj[],int n,vector <int> indegree){
queue<int> q;
vector <int> topo;
for (int i = 0; i < n; i++)
if (indegree[i] == 0) q.push(i);
while(q.size()>0){
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 main(){
int n,m;
cin>>n>>m;
vector <int> adj[n];
vector <int> indegree(n,0);
int a,b;
for(int i = 0; i<m ; i++){
cin >> a >> b;
adj[a].push_back(b);
indegree[b]++;
}
vector <int> res = topoSort(adj,n,indegree);
for(int i{0};i<res.size();i++){
cout<<res[i]<<" ";
}
return 0;
}