making bridge tree added

Author: sayedppqq

Graph/Making Bridge Tree.cpp

@@ -0,0 +1,141 @@
+#include<bits/stdc++.h>
+#include<ext/pb_ds/assoc_container.hpp>
+#include<ext/pb_ds/tree_policy.hpp>
+#define  FIO        ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+#define  Fileio     freopen("output.txt","w",stdout);freopen("input.txt","r",stdin);
+#define  all(v)     v.begin(),v.end()
+#define  rall(v)    v.rbegin(),v.rend()
+#define  MEM(a,x)   memset(a,x,sizeof(a))
+#define  SZ(v)      v.size()
+#define  nl         "\n"
+#define  bug        cout<<"bug"<<nl;
+#define  pi         acos(-1.0)
+#define  ll     long long
+#define  pb     push_back
+#define  mp     make_pair
+#define  pii    pair< int,int >
+#define  pll    pair< ll,ll >
+#define  vii    vector< int >
+#define  vll    vector< ll >
+#define  vpi    vector< pii >
+#define  vpl    vector<pll>
+#define  MX     100005
+#define  EPS    1e-12
+#define  ss     second
+#define  ff     first
+using namespace std;
+using namespace __gnu_pbds;
+
+template<typename T>
+using ordered_set=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
+template<typename T>
+using ordered_multiset=tree<T, null_type, less_equal<T>, rb_tree_tag,tree_order_statistics_node_update>;
+
+inline ll powr(int a,int b){ll res=1;while(b){if(b&1) res*=a;a*=a;b/=2;}return res;}
+int cases=1;
+
+#ifdef ppqq
+     #define debug(...) __f(#__VA_ARGS__, __VA_ARGS__)
+    template < typename Arg1 >
+    void __f(const char* name, Arg1&& arg1){
+        cerr << name << " is " << arg1 << std::endl;
+    }
+    template < typename Arg1, typename... Args>
+    void __f(const char* names, Arg1&& arg1, Args&&... args){
+        const char* comma = strchr(names+1, ',');
+        cerr.write(names, comma - names) << " is " << arg1 <<"  ";
+        __f(comma+1, args...);
+    }
+#else
+    #define debug(...)
+#endif
+
+///******************************************START******************************************
+
+///Source : https://codeforces.com/blog/entry/83980
+
+vector<pair<int,int>> adj[100005];
+vector<int>bridge_tree[100005],in_time,low;
+vector<pair<int,int>>edges;
+vector<bool> vis;
+bool isBridge[100005];
+int timer,n,m,grp[100005],id;
+void dfs(int u,int p)
+{
+    in_time[u]=low[u]=timer++;
+    vis[u]=true;
+
+    for(auto it: adj[u])
+    {
+        if(it.ff==p) continue;
+        if(vis[it.ff])
+            low[u]=min(in_time[it.ff],low[u]);
+        else
+        {
+            dfs(it.ff,u);
+            low[u]=min(low[u],low[it.ff]);
+            if(low[it.ff]>in_time[u])
+                isBridge[it.ss]=true;
+        }
+    }
+}
+void findBridges()
+{
+    in_time.assign(n+2,0);
+    low.assign(n+2,0);
+    vis.assign(n+2,false);
+    timer=1;
+    for(int i=1;i<=n;i++)
+        if(!vis[i]) dfs(i,-1);
+}
+void dfs2(int u,int p)
+{
+    vis[u]=true;
+    grp[u]=id;
+    for(auto it: adj[u])
+    {
+        if(vis[it.ff] || isBridge[it.ss]) continue;  ///avoiding if its a bridge
+        dfs2(it.ff,u);
+    }
+}
+void givingGroupNumber()
+{
+    vis.clear();vis.assign(n+2,false);
+    for(int i=1;i<=n;i++)
+    {
+        if(!vis[i])
+        {
+            id++;
+            dfs2(i,-1);
+        }
+    }
+}
+void makeBridgeTree()
+{
+    findBridges();
+    givingGroupNumber();
+
+    for(int i=1;i<=m;i++)
+    {
+        if(isBridge[i])
+        {
+            bridge_tree[grp[edges[i-1].ff]].pb(grp[edges[i-1].ss]);
+            bridge_tree[grp[edges[i-1].ss]].pb(grp[edges[i-1].ff]);
+        }
+    }
+}
+int main()
+{
+    FIO;
+    cin>>n>>m;
+    for(int i=1,u,v;i<=m;i++)
+    {
+        cin>>u>>v;
+        adj[u].pb({v,i});
+        adj[v].pb({u,i});
+        edges.pb({u,v});
+    }
+
+    makeBridgeTree();
+
+}