Graph

Author: pranavbharadwaj007

CSES-Problem-Set/course-schedule.cpp

@@ -0,0 +1,69 @@
+#include<bits/stdc++.h>
+using namespace std;
+#define int long long
+const int N=1e5+10;
+const int INF=1e18;
+int n,m;
+vector<int>adj[N];
+bool detectCycle(vector<int>&vis,int v){
+if(vis[v]==2)return true;
+vis[v]=2;
+for(auto it:adj[v]){
+  if(vis[it]!=1){
+    if(detectCycle(vis,it)){
+      return true;
+    }
+  }
+}
+  vis[v]=1;
+  return false;
+}
+bool cycleDect(int n){
+  vector<int> vis(n+1,0);
+  for(int i=0;i<n;i++){
+    if(!vis[i]){
+      if(detectCycle(vis, i)){
+        return true;
+      }
+    }
+  }
+  return false;
+}
+void topoDfs(int v,vector<int>& visited,vector<int>& res){
+   visited[v]=1;
+   for(auto it:adj[v]){
+     if(!visited[it]){
+       topoDfs(it,visited, res);
+     }
+   }
+res.push_back(v);
+}
+signed main() {
+cin>>n>>m;
+vector<pair<int,int>>g[n+1];
+for(int i=0;i<m;i++){
+  int x,y,wt;
+  cin>>x>>y;
+  adj[x].push_back(y);
+}
+bool isCy=cycleDect(n);
+if(isCy){
+  cout<<"IMPOSSIBLE"<<endl;
+}
+else{
+ vector<int> visited(n+5,0);
+ vector<int>res;
+ for(int i=1;i<=n;i++){
+   if(!visited[i]){
+   topoDfs(i,visited,res);
+   }
+ }
+ reverse(res.begin(),res.end());
+ for(auto y:res){
+   cout<<y<<" ";
+ }
+ cout<<endl;
+}
+ return 0;
+}
+