Merge pull request larissalages#224 from Aman2632/master

AmanMishra.md

Author: larissalages

classical_algorithms/c++/DSU_implementation.cpp

@@ -0,0 +1,104 @@
+// D-S-U -> disjoint set and union.....implementation
+
+#include <bits/stdc++.h>
+using namespace std;
+
+typedef long long int ll;
+using ii= pair<ll,ll>;
+#define F first
+#define S second
+#define MP make_pair
+#define PB push_back
+//using min_of_3=min({ll a,ll b,ll c});
+
+ll parent[1001];
+ll size[1001];
+vector<ii> build;       // roads to be built
+vector<ii> demo;      // roads to be demolished
+
+void make_set(ll v)
+{
+    parent[v]=v;
+    size[v]=1;
+}
+
+ll find_set(ll v)         // In find_set(v) we actually find the representative or root of the subtree having node v..
+{                         // As an optimization we use...COMPRESSION BY PATH ...where after finding a certain v...we set
+    if(parent[v]==v)      // v's parent directly to its representative so as to shorten the path for future find_set calls...
+    {
+        return v;
+    }
+    else
+    {
+        return parent[v]=find_set(parent[v]);    // be ware ...if you write parent[v]=find_set(parent[v])...you may get error/TLE
+    }
+}
+
+
+void union_set(ll u,ll v)  // UNION OR MERGING 2 CONNECTED COMPONENTS TOGETHER...
+{
+    u= find_set(u);
+    v= find_set(v);
+    
+    if(u!=v)
+    {
+        if(size[u]<size[v])     // UNION BY SIZE OPTIMIZATION-> attach the tree with lower size to the tree with bigger size...
+        {                       // So that the size of tree may not grow much
+            swap(u,v);
+        }
+        parent[v]=u;
+        size[u]+=size[v];
+    }
+}
+
+
+
+
+int main()
+{
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);cout.tie(NULL);
+	
+    ll n;
+    cin>>n;
+    ll m=n-1;
+    
+    for(ll i=1;i<=n;i++)
+    {
+        make_set(i);
+    }
+    
+    while(m--)
+    {
+        ll a,b;
+        cin>>a>>b;
+        
+        if(find_set(a)==find_set(b))
+        {
+            demo.PB({a,b});
+        }
+        else
+        {
+            union_set(a,b);
+        }
+    }
+    
+	for(ll i=2;i<=n;i++)
+	{
+	    if(find_set(i)!=find_set(1))
+	    {
+	        build.PB({i,1});
+	        union_set(i,1);
+	    }
+	}
+	
+	ll x=build.size();
+	cout<<build.size()<<"\n";
+	
+	for(ll i=0;i<x;i++)
+	{
+	    cout<<demo[i].F<<" "<<demo[i].S<<" "<<build[i].F<<" "<<build[i].S<<"\n";
+	}
+	
+	
+}