void AddEpsilonTransition(int left, int right)
        {
            pairStates temp;
            temp.leftState = left;
            temp.rightState = right;
            epsilonTransitions.Add(temp);
        }

        void AddTransition(int left, int right, char c)
        {
            Transitions.Add(left.ToString() + "," + c, right);
        }

        int newState()
        {
            this.numStates++;
            return this.numStates - 1;
        }

        bool isOperator(string expression, int i)
        {
            int num = 0;
            while(i - 1 >= 0 && expression[i-1] == '\\')
            {
                num++;
                i--;
            }
            return num % 2 == 0;
        }

        int findPar(string expression, int i)
        {
            int num = 0;
            for (; i < expression.Length; i++)
            {
                if (expression[i] == '(') num++;
                else if (expression[i] == ')') num--;
                if (num == 0) return i;
            }
            return -1;
        }

        pairStates convert(string expression)
        {
            List<string> selection = new List<string>();
            int numPar = 0;
            int j = 0;
            int i = 0;
            for (; i < expression.Length; i++)
            {
                if (expression[i] == '(' && isOperator(expression, i)) numPar++;
                else if (expression[i] == ')' && isOperator(expression, i)) numPar--;
                else if(numPar == 0 && expression[i] == '|' && isOperator(expression,i))
                {
                    selection.Add(expression.Substring(j,i-j));
                    j = i + 1;
                }
            }
            if (selection.Count() > 0) selection.Add(expression.Substring(j, i - j));

            int leftState = newState();
            int rightState = newState();

            if (selection.Count() > 0)
                for (i = 0; i < selection.Count; i++)
                {
                    pairStates temp = convert(selection[i]);
                    AddEpsilonTransition(leftState, temp.leftState);
                    AddEpsilonTransition(temp.rightState, rightState);
                }
            else
            {
                bool prefix = false;
                int lastState = leftState;
                for (i = 0; i < expression.Length; i++)
                {
                    int a, b;
                    if (prefix == true)
                    {
                        prefix = false;
                        char transition;
                        if (expression[i] == 't') transition = '\t';
                        else if (expression[i] == 'n') transition = '\n';
                        else if (expression[i] == '_') transition = ' ';
                        else transition = expression[i];
                        a = newState();
                        b = newState();
                        AddTransition(a, b, transition);
                    }
                    else
                    {
                        if (expression[i] == '\\')
                        {
                            prefix = true;
                            continue;
                        }
                        if (expression[i] != '(')
                        {
                            a = newState();
                            b = newState();
                            if( expression[i] == '$') AddEpsilonTransition(a,b);
                            else AddTransition(a,b,expression[i]);
                        }
                        else
                        {
                            j = findPar(expression,i);
                            pairStates temp = convert(expression.Substring(i+1,j-i-1));
                            a = temp.leftState;
                            b = temp.rightState;
                            i = j;
                        }
                    }
                    if (i + 1 < expression.Length && expression[i + 1] == '*')
                    {
                        int x = a;
                        int y = b;
                        a = newState();
                        b = newState();
                        AddEpsilonTransition(a,x);
                        AddEpsilonTransition(y, b);
                        AddEpsilonTransition(a, b);
                        AddEpsilonTransition(y, x);
                        i++;
                    }
                    AddEpsilonTransition(lastState, a);
                    lastState = b;
                }
                AddEpsilonTransition(lastState, rightState);
            }
            pairStates temp2;
            temp2.leftState = leftState;
            temp2.rightState = rightState;
            return temp2;
        }