Created
August 14, 2019 05:21
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| #include<bits/stdc++.h> | |
| using namespace std; | |
| typedef unsigned long long int ll; | |
| const int mx=1e4+1; | |
| vector<int>v[mx]; | |
| int cont=0; | |
| bool vis1[mx]; | |
| bool vis2[mx]; | |
| bool cyclic(int u,int parent,bool vis[]) | |
| { | |
| vis[u]=true; | |
| for(int i=0;i<v[u].size();i++) | |
| { | |
| if(!vis[v[u][i]]) | |
| { | |
| if(cyclic(v[u][i],u,vis)) | |
| { | |
| return true; | |
| } | |
| } | |
| else if(v[u][i]!=parent) | |
| { | |
| return true; | |
| } | |
| } | |
| return false; | |
| } | |
| void dfs(int u,bool vis[]) | |
| { | |
| vis[u]=true; | |
| for(int i=0;i<v[u].size();i++) | |
| { | |
| if(!vis[v[u][i]]) | |
| { | |
| dfs(v[u][i],vis); | |
| } | |
| } | |
| } | |
| int main() | |
| { | |
| ios::sync_with_stdio(false); | |
| cin.tie(NULL); | |
| cout.tie(NULL); | |
| memset(vis1,false,sizeof(vis1)); | |
| memset(vis2,false,sizeof(vis2)); | |
| int n,m,a,b; | |
| cin>>n>>m; | |
| while(m--) | |
| { | |
| cin>>a>>b; | |
| v[a].push_back(b); | |
| v[b].push_back(a); | |
| } | |
| bool cycle=false; | |
| for(int i=1;i<=n;i++) | |
| { | |
| if(!vis1[i]) | |
| { | |
| if(cyclic(i,-1,vis1)) | |
| { | |
| cycle=true; | |
| } | |
| } | |
| } | |
| dfs(1,vis2); | |
| bool disconnected=false; | |
| for(int i=1;i<=n;i++) | |
| { | |
| if(vis2[i]==false) | |
| { | |
| disconnected=true; | |
| } | |
| } | |
| if(cycle||disconnected) | |
| { | |
| cout<<"NO"<<endl; | |
| } | |
| else{ | |
| cout<<"YES"<<endl; | |
| } | |
| } |
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