diff --git a/chessboard.cpp b/chessboard.cpp
new file mode 100644
index 0000000..5a4acc3
--- /dev/null
+++ b/chessboard.cpp
@@ -0,0 +1,91 @@
+#include <iostream>
+#include <iomanip>
+#include <stdexcept>
+using namespace std;
+
+class ChessBoardArray {
+  protected:
+  class Row {
+    public:
+    Row(ChessBoardArray &a, int i):chessBoardArray(a), row(i) {}
+    int & operator [] (int i) const{
+      return chessBoardArray.select(row, i);
+    }
+    
+    private:
+    ChessBoardArray &chessBoardArray;
+    int row;
+  };
+  class ConstRow {
+    public:
+    ConstRow(const ChessBoardArray &a, int i) : chessBoardArray(a), row(i) {};
+    int operator [] (int i) const {
+      return chessBoardArray.select(row, i);
+    }
+
+    private:
+    const ChessBoardArray &chessBoardArray;
+    int row;
+  };
+
+  public:
+    ChessBoardArray(unsigned size=0, unsigned base=0) : data(new int[(size*size+1)/2]), thebase(base), thesize(size) {}
+    
+    ChessBoardArray(const ChessBoardArray &a) : data(new int[(a.thesize*a.thesize+1)/2]), thebase(a.thebase), thesize(a.thesize) {
+      for(unsigned i=0; i<((thesize*thesize+1)/2); ++i) data[i]=a.data[i];
+      }
+
+    ~ChessBoardArray() {delete [] data;}
+
+    ChessBoardArray & operator = (const ChessBoardArray &a) {
+      delete [] data;
+      thebase=a.thebase;
+      thesize=a.thesize;
+      data=new int[(thesize*thesize+1)/2];
+      for(unsigned i=0; i<((thesize*thesize+1)/2); ++i) data[i]=a.data[i];
+      return *this;
+      }
+
+    int & select(int i, int j) {
+      return data[loc(i,j)];
+    }
+    int select(int i, int j) const {
+      return data[loc(i,j)];
+    }
+
+    const Row operator [] (int i) {
+      return Row(*this,  i);
+    }
+    const ConstRow operator [] (int i) const {
+      return ConstRow(*this, i);
+    }
+
+    friend ostream & operator << (ostream &out, const ChessBoardArray &a) {
+    	for(int line=0; line<a.thesize; ++line) {
+    		for(int sthlh=0; sthlh<a.thesize; ++sthlh) {
+    			cout<<setw(4);
+    			if((line+sthlh)%2==0) 
+    				cout<<a.select(line+a.thebase,sthlh+a.thebase);
+    			else cout<<0;
+    		}
+    		cout<<endl;
+    	}
+    	return out;
+    }
+      
+    
+    protected:
+    int *data;
+    int thebase;
+    unsigned thesize;
+
+    unsigned int loc(int i, int j) const throw(out_of_range) {
+      int di=i-thebase, dj=j-thebase;
+      if(di<0 || di>=thesize || dj<0 || dj>=thesize || (i+j)%2==1) throw out_of_range("invalid index");
+      return (di*thesize +dj)/2;
+    }
+
+};
+
+ 
+
diff --git a/cycle.cpp b/cycle.cpp
new file mode 100644
index 0000000..449496c
--- /dev/null
+++ b/cycle.cpp
@@ -0,0 +1,66 @@
+#include <iostream>
+#include <list>
+#include <vector>
+#include <algorithm> 
+using namespace std;
+
+class Graph{
+  private:
+  int numofvertices; 
+  list<int> *ptr;
+  vector<int> color;
+  vector<int> root;
+  int startofcircle, endofcircle;
+
+  bool DFS(int v) {
+    color[v]=1;
+    for(int u: ptr[v]){
+      if(color[u]==0) {
+        root[u]=v;
+        if(DFS(u))
+        return true;
+      }
+      else if(color[u]==1) {
+        endofcircle=v;
+        startofcircle=u;
+        return true;
+      }
+    } 
+    color[v]=2;
+    return false;
+  }
+
+  
+  public:
+
+  Graph(int V): numofvertices(V) { ptr=new list<int>[numofvertices]; }
+
+  ~Graph() { delete [] ptr;}
+
+  void addEdge (int u, int v) {
+    ptr[u].push_back(v);
+  }
+
+  bool cycle(vector<int> &cycle) {
+    color.assign(numofvertices, 0);
+    root.assign(numofvertices, -1);
+    startofcircle=-1;
+
+    for(int v=0; v<numofvertices; v++) {
+      if(color[v]==0 && DFS(v))
+      break;
+    }
+
+    if(startofcircle==-1)
+    return false;
+    else {
+      cycle.push_back(startofcircle);
+      for( int v=endofcircle; v!=startofcircle; v=root[v])
+      cycle.push_back(v);
+
+      reverse(cycle.begin(), cycle.end());
+      return true;
+    }
+  }
+};
+
diff --git a/euler.cpp b/euler.cpp
new file mode 100644
index 0000000..be642e3
--- /dev/null
+++ b/euler.cpp
@@ -0,0 +1,71 @@
+#include <iostream>  
+#include <string>  
+#include <array>  
+using namespace std;  
+
+
+int main() {  
+
+
+  int N;
+  int M;
+  int u, v; 
+  int per=0;  
+  int pathpart[4];  
+
+  cin>>N;  
+  cin>>M;  
+
+  int nodevalue[N];  
+
+  for (int i=0; i<N; i++) {  
+    nodevalue[i]=0;  
+  }  
+
+  for(int i=0; i<M; i++) {  
+    cin>>u;  
+    cin>>v;  
+    nodevalue[u]++;  
+    nodevalue[v]++;  
+  }  
+  for (int j=0; j<N; j++) {  
+    if (nodevalue[j]%2!=0) {  
+      pathpart[per]=j;  
+      per++;  
+      if (per>2){  
+        cout<<"IMPOSSIBLE";  
+        cout<<endl;  
+        exit(0);  
+      }  
+    }  
+  }  
+
+  if (per==0) {  
+    cout<< "CYCLE";  
+    cout<<endl;  
+  }  
+
+  else if (per==2) {  
+    cout<< "PATH ";  
+
+    if (pathpart[0]<pathpart[1]) {  
+      cout<<pathpart[0];  
+      cout<<" ";  
+      cout<<pathpart[1];  
+      cout<<endl;  
+    }  
+
+    else {  
+      cout<<pathpart[1];  
+      cout<<" ";  
+      cout<<pathpart[0];  
+      cout<<endl;  
+    }  
+  }  
+  
+  else {  
+    cout<<"IMPOSSIBLE";  
+    cout<<endl;  
+  }  
+}
+
diff --git a/fullratio.cpp b/fullratio.cpp
new file mode 100644
index 0000000..e3828e0
--- /dev/null
+++ b/fullratio.cpp
@@ -0,0 +1,87 @@
+#include <iostream>  
+#ifndef CONTEST  
+#include "fullratio.hpp"  
+#endif  
+using namespace std;  
+  
+std::ostream& operator << (std::ostream &out, const rational &x) {  
+     out<<x.nom<<"/"<<x.den;  
+     return out;  
+ }  
+  
+  
+int rational::gcd(int a, int b) {    
+  if(a<0) a=(-1)*a;    
+  if(b<0) b=(-1)*b;    
+          
+  while(a>0 && b>0) {    
+    if(a>b) a=a%b;    
+    else b=b%a;    
+  }    
+  return a+b;    
+}  
+  
+rational::rational (int n, int d) {    
+  int mkd=gcd(n, d);    
+  nom=n/mkd;    
+  den=d/mkd;    
+  if(den<0){    
+    nom=(-1*nom);    
+    den=(-1*den);    
+  }    
+}  
+  
+rational operator + (const rational &x, const rational &y) {  
+  int arithm=((x.nom)*(y.den))+((y.nom)*(x.den));    
+  int parono=((x.den)*(y.den));  
+    
+  int a=arithm;  
+  int b=parono;  
+  if(a<0) a=(-1)*a;  
+  if(b<0) b=(-1)*b;  
+    
+  int c=rational::gcd(a,b);
+  return ( rational(arithm/c, parono/c) );    
+}    
+  
+  
+rational operator - (const rational &x, const rational &y) {  
+  int arithm=((x.nom)*(y.den))-((y.nom)*(x.den));  
+  int parono=((x.den)*(y.den));  
+  
+  int a=arithm;  
+  int b=parono;  
+  if(a<0) a=(-1)*a;  
+  if(b<0) b=(-1)*b;  
+  
+  int c=rational::gcd(a,b);
+  
+  return ( rational(arithm/c, parono/c) );  
+}  
+  
+rational operator * (const rational &x, const rational &y) {  
+  int arithm=((x.nom)*(y.nom));  
+  int parono=((x.den)*(y.den));  
+  int a=arithm;  
+  int b=parono;  
+  if(a<0) a=(-1)*a;  
+  if(b<0) b=(-1)*b;  
+
+  int c=rational::gcd(a,b);             
+  
+  return ( rational(arithm/c, parono/c) );  
+}  
+  
+rational operator / (const rational &x, const rational &y) {  
+  int arithm=((x.nom)*(y.den));  
+  int parono=((x.den)*(y.nom));  
+  int a=arithm;  
+  int b=parono;  
+  if(a<0) a=(-1)*a;  
+  if(b<0) b=(-1)*b;  
+
+  int c=rational::gcd(a,b); 
+  
+  return ( rational(arithm/c, parono/c) );  
+}  
+
diff --git a/lexicon.cpp b/lexicon.cpp
new file mode 100644
index 0000000..9b0c63d
--- /dev/null
+++ b/lexicon.cpp
@@ -0,0 +1,212 @@
+ 
+
+class lexicon  
+{  
+    private:  
+    class Node  
+    {  
+        public:  
+        std::string key;  
+        Node* left=nullptr;  
+        Node* right=nullptr;  
+        int freq=1; 
+    };  
+
+    Node* root;  
+    public:  
+
+    lexicon():root(nullptr){}  
+
+    ~lexicon(){purge(root);}  
+    
+    void purge(Node* root)  
+    {  
+        if(root==nullptr)  
+            return;  
+        purge(root->left);  
+        purge(root->right);  
+        delete root;  
+    }  
+    Node* createNode(const std::string &s)  
+    {  
+        Node* newNode = new Node();  
+        newNode->key=s;  
+        newNode->left=newNode->right=nullptr;  
+        newNode->freq = 1;  
+        return newNode;  
+    }  
+ 
+    void insert(const std::string &s)  
+    {  
+        if(root==nullptr)  
+        {  
+            root=createNode(s);  
+        }else if(insert(root,s)){}  
+    }  
+    bool insert(Node* t, const std::string &s)  
+    {  
+        if(s<t->key)  
+        {  
+            if(t->left==nullptr)  
+            {  
+                t->left=createNode(s);  
+                return true;  
+            }else  
+                return insert(t->left,s);  
+        }else if(s>t->key)  
+        {  
+            if(t->right==nullptr)  
+            {  
+                t->right=createNode(s);  
+                return true;  
+            }else  
+                return insert(t->right,s);  
+        }else  
+        {  
+        ++(t->freq);  
+        return false;  
+        }  
+    }  
+    int lookup(const std::string &s) const  
+    {  
+        return lookup(root,s);  
+    }  
+    Node* minVal(Node* root)  
+    {  
+        Node* temp = root;  
+        while(temp->left!=nullptr)  
+            temp= temp->left;  
+        return temp;  
+    }  
+    void remove(const std::string & s)  
+    {  
+        root=remove(root,s);  
+    }  
+    Node* remove(Node* root, const std::string &s)  
+    {  
+        if(root==nullptr)  
+            return root;  
+        if(s<root->key)  
+            root->left=remove(root->left,s);  
+        else if(s>root->key)  
+            root->right=remove(root->right,s);  
+        else   
+        {  
+            if(root->left==nullptr)  
+            {  
+                Node* temp= root->right;  
+                delete root;  
+                return temp;  
+            }  
+            if(root->right==nullptr)  
+            {  
+                Node* temp = root->left;  
+                delete root;  
+                return temp;  
+            }  
+        Node* temp = minVal(root->left);  
+        root->key=temp->key;  
+        root->freq=temp->freq;  
+        root->left=remove(root->left,temp->key);  
+    }  
+    return root;  
+    }
+
+    int lookup(Node* root, const std::string& s) const  
+    {  
+    
+        if(root==nullptr)  
+            return 0;  
+        if(s==root->key)  
+            return root->freq;  
+        else if(s<root->key)  
+            return lookup(root->left,s);  
+        else if(s>root->key)  
+            return lookup(root->right,s);  
+    } 
+
+    void Inorder()const  
+    {  
+        Inorder(root);  
+    }  
+    void Inorder(Node* root)const  
+    {  
+        if(root==nullptr)  
+            return;  
+        Inorder(root->left);  
+        cout<<root->key<<" "<<root->freq<<endl;  
+        Inorder(root->right);  
+    }  
+    
+    void replace(const string &s1, const string &s2)  
+    {  
+        
+        if(lookup(s1)==0)  
+            return;  
+        else  
+        {  
+            int s1_freq=0;  
+            Node*node_1=search_string(s1);  
+            s1_freq=node_1->freq;  
+            remove(s1);  
+            if(lookup(s2)==0) 
+            {  
+                insert(s2);  
+                
+                search_string(s2)->freq=s1_freq;  
+            }else  
+                search_string(s2)->freq+=s1_freq;  
+        }  
+        
+    }  
+    friend ostream& operator<<(ostream& stream, const lexicon& l)  
+    {  
+        l.Inorder(l.root);  
+        stream<<"";  
+        return stream;  
+    }  
+    Node* search_string(const std::string &s)  
+    {  
+        return search_string(root,s);  
+    }  
+    Node* search_string(Node* root,const std::string &s)  
+    {  
+        if(root==nullptr || s==root->key)  
+            return root;  
+        else if(s<root->key)  
+            return search_string(root->left,s);  
+        else if(s>root->key)  
+            return search_string(root->right,s);  
+    }  
+int getLevelUtil(Node* root  ,const string& data, int level) const  
+{   
+    if (root == nullptr)   
+        return 0;   
+    if (root -> key == data)   
+        return level;   
+    int downlevel = getLevelUtil(root -> left,    
+                                 data, level + 1);   
+    if (downlevel != 0)   
+        return downlevel;   
+    downlevel = getLevelUtil(root->right,    
+                             data, level + 1);   
+    return downlevel;   
+}   
+int depth( const string &s) const  
+{   
+    return getLevelUtil(root, s, 1);   
+}   
+void print()  
+{  
+    cout<<root->key<<endl;  
+}     
+   
+};
+
+#include <iostream>  
+#include <string>  
+#include <list>
+#include <array>
+#include <vector>
+#include <algorithm>
+using namespace std; 
diff --git a/polynomial.cpp b/polynomial.cpp
new file mode 100644
index 0000000..7e95502
--- /dev/null
+++ b/polynomial.cpp
@@ -0,0 +1,254 @@
+#include <iostream>
+using namespace std;
+
+class Polynomial {
+  public:
+  class Term {
+    public:
+    int exponent;
+    int coefficient;
+    Term *next;
+    protected:
+    Term(int exp, int coeff, Term *n) : exponent(exp), coefficient(coeff), next(n){}; 
+    friend class Polynomial;
+  };
+
+  Term *head;
+  int degree;
+  int size;
+
+  Polynomial():head(nullptr), degree(0), size(0) {}
+  Polynomial(const Polynomial &p): head(nullptr), degree(0), size(0) {copy(p);};
+  ~Polynomial() {purge();}
+
+  Polynomial & operator =(const Polynomial &p) {clear(); copy(p); return *this;}
+  
+  void purge() { 
+    Term *l=head;
+    degree=0;
+    size=0;
+    while(l!=nullptr) {
+      Term *q=l;
+      l=l->next;
+      delete q;
+    }
+  }
+
+    void clear() {
+    purge();
+    head=nullptr;
+    degree=0;
+    size=0;
+  }
+
+  void remove(int exp) /* AFAIREI STOIXEIO*/ {  
+    Term* temp=head;  
+    Term* prev;  
+    if(head==nullptr) return; 
+    else {  
+      if(head->exponent==exp) {  
+        head=head->next;  
+        delete temp;  
+      }
+      else {  
+        for(temp = head;temp->next!=nullptr && temp->exponent !=exp;temp = temp->next) {  
+          prev=temp;  
+        }  
+        if(temp->exponent==exp) {  
+          prev->next = temp->next;  
+          delete temp;  
+        }
+        else  return;  
+      }  
+      --size;  
+    }  
+  }
+
+
+
+  void addTerm(int expon, int coeff) {  
+    if(coeff==0 || expon<0) return;  
+    Term *newTerm = new Term(expon,coeff,nullptr);  
+    Term *temp = head;  
+    if(expon>degree) degree=expon;  
+    if(head==nullptr) {  
+      newTerm->next=nullptr;  
+      head=newTerm;  
+      ++size;  
+      return;  
+    }  
+    if(expon>head->exponent) {  
+      newTerm->next=head;  
+      head=newTerm;  
+      ++size;  
+      return;  
+    }  
+    if(expon==head->exponent) /* HERE */ {  
+      head->coefficient=head->coefficient+newTerm->coefficient;  
+      if(head->coefficient==0) remove(head->exponent);  
+      return;  
+    }  
+    while(temp->next!=nullptr) {  
+      if(expon==temp->exponent) /*here*/ {  
+        temp->coefficient=temp->coefficient+newTerm->coefficient;  
+        if(temp->coefficient==0)  
+        remove(temp->exponent); 
+        return;  
+      }  
+      if(expon>temp->next->exponent) {  
+        newTerm->next = temp->next;  
+        temp->next = newTerm;  
+        return;  
+      }  
+     temp = temp->next;  
+    }  
+    if(newTerm->exponent==temp->exponent) /*HERE*/ {  
+      temp->coefficient=temp->coefficient + newTerm->coefficient;  
+      if(temp->coefficient==0) remove(temp->exponent);  
+      return;  
+    }  
+    else {  
+      newTerm->next=nullptr;  
+      temp->next=newTerm;  
+      //temp->coefficient=temp->coefficient+newTerm->coefficient;  
+      ++size;  
+    }  
+    return;  
+  }  
+
+  double evaluate(double x) {
+    double sum=0;
+    int exp;
+    for(Term *l=head; l!=nullptr; l=l->next) {
+      exp=l->exponent;
+      double expvalue=1;
+      if (exp==0) expvalue=1;
+      else {
+        for(int i=0; i<exp; ++i) {
+        expvalue*=x;
+        }
+      }
+      sum+=(l->coefficient)*expvalue;
+    }
+    return sum;
+  }
+
+  friend Polynomial operator+ (const Polynomial &p, const Polynomial &q) {  
+    Polynomial r;  
+    Polynomial::Term *temp_p = p.head;  
+    Polynomial::Term *temp_q = q.head;  
+    while(!(temp_p==nullptr && temp_q ==nullptr)) {  
+      if(temp_p==nullptr && temp_q!=nullptr) {  
+        r.addTerm(temp_q->exponent,temp_q->coefficient);  
+        temp_q=temp_q->next;  
+        continue;  
+      }  
+      if(temp_q==nullptr && temp_p!=nullptr) {  
+        r.addTerm(temp_p->exponent,temp_p->coefficient);  
+        temp_p=temp_p->next;  
+        continue;  
+      }  
+      if(temp_p->exponent == temp_q->exponent) {  
+        r.addTerm(temp_p->exponent,temp_p->coefficient + temp_q ->coefficient);  
+        temp_p=temp_p->next;  
+        temp_q=temp_q->next;  
+      }  
+      else if(temp_p->exponent > temp_q ->exponent ) {  
+        r.addTerm(temp_p->exponent, temp_p->coefficient);  
+        temp_p=temp_p->next;  
+      }
+      else if(temp_p->exponent < temp_q->exponent) {  
+        r.addTerm(temp_q->exponent,temp_q->coefficient);  
+        temp_q = temp_q->next;  
+      }  
+    }  
+    return r;  
+}
+  friend Polynomial operator* (const Polynomial &p, const Polynomial &q) {  
+    Polynomial r[p.size+q.size+30];  
+    Polynomial product;  
+    int counter=0;  
+    for(Polynomial :: Term *i = p.head; i!=nullptr; i = i->next) {  
+      for(Polynomial :: Term * j= q.head; j!=nullptr; j = j->next) {  
+          r[counter].addTerm(i->exponent+j->exponent, (i->coefficient)*(j->coefficient));  
+      }  
+      //cout<<r[counter];  
+      ++counter;  
+    }  
+    product = r[0];  
+    for(int i=1;i<counter;i++) {  
+      product = product + r[i];  
+    }  
+    return product;  
+}
+
+  friend ostream & operator << (ostream &out, const Polynomial &p) {
+    if(p.head==nullptr) {  
+      out<<"0";  
+      return out;  
+    }  
+    for(Polynomial::Term *i = p.head;i!=nullptr;i=i->next) {  
+      if(i==p.head) {  
+        if(i->exponent==0) {  
+          if(i->coefficient < 0) out<<"- "<<-(i->coefficient);  
+          else if(i->coefficient > 0) out<<i->coefficient;  
+        }
+        else if(i->exponent==1) {  
+          if(i->coefficient < 0) {  
+            if(i->coefficient==-1) out<<"- "<<"x";  
+            else  out<<"- "<<-(i->coefficient)<<"x";  
+          }  
+          else if(i->coefficient > 0) {  
+            if(i->coefficient==1) out<<"x";  
+            else out<<i->coefficient<<"x";  
+          }  
+        }
+        else if(i->exponent > 1) {  
+          if(i->coefficient < 0) {  
+            if(i->coefficient==-1) out<<"- "<<"x^"<<i->exponent;  
+            else out<<"- "<<-(i->coefficient)<<"x^"<<i->exponent;  
+          }
+          else if(i->coefficient > 0) {  
+            if(i->coefficient==1) out<<"x^"<<i->exponent;  
+            else out<<i->coefficient<<"x^"<<i->exponent;  
+          }  
+        }  
+      }  
+      else {  
+        if(i->exponent==0) {  
+          if(i->coefficient < 0) out<<" - "<<-(i->coefficient);  
+          else if(i->coefficient > 0) out<<" + "<<i->coefficient;   
+        }
+        else if(i->exponent==1) {  
+          if(i->coefficient < 0) {  
+            if(i->coefficient==-1) out<<" - "<<"x";  
+            else out<<" - "<<-(i->coefficient)<<"x";  
+          }  
+          else if(i->coefficient > 0) {  
+            if(i->coefficient==1) out<<" + "<<"x";  
+            else out<<" + "<<i->coefficient<<"x";  
+          }  
+        }
+        else if(i->exponent > 1) {  
+          if(i->coefficient < 0) {  
+           if(i->coefficient==-1) out<<" - "<<"x^"<<i->exponent;  
+           else out<<" - "<<-(i->coefficient)<<"x^"<<i->exponent;  
+          }  
+          else if(i->coefficient > 0) {  
+            if(i->coefficient==1) out<<" + "<<"x^"<<i->exponent;  
+            else out<<" + "<<i->coefficient<<"x^"<<i->exponent;  
+          }  
+        }  
+      }  
+    }  
+    //out<<"\n";  
+    return out;  
+  }
+
+  private: 
+   void copy(const Polynomial &p) {
+    for(Term *l=p.head; l!=nullptr; l=l->next) addTerm(l->exponent, l->coefficient);
+   }
+};
+
+