public RPN(ArrayList query, Fleet fleet)
{
// Define valid tokens
operators = new ArrayList();
operands = new ArrayList();
// Here we hardcode operators. Although operands takes from vehicleattribute list
string[] op1 = { "AND", "OR", "(", ")" }; // operators and parentheses
operators.AddRange(op1);
string[] op2 = fleet.VehicleAttributes.ToArray(); // operands
operands.AddRange(op2);
// Create and instantiate a new empty Stack.
Stack rpnStack = new Stack();
// Apply dijkstra algorithm using a stack to convert infix to postfix notation (=rpn)
InfixTokens.AddRange(query);
foreach (string token in InfixTokens)
{
if (operands.Contains(token))
{ // Move operands across to output
PostfixTokens.Add(token);
}
else if (token.Equals("("))
{ // Push open parenthesis onto stack
rpnStack.Push(token);
}
else if (token.Equals(")"))
{ // Pop all operators off the stack until the mathcing open parenthesis is found
while ((rpnStack.Count > 0) && !((string)rpnStack.Peek()).Equals("("))
{
PostfixTokens.Add(rpnStack.Pop()); // transfer operator to output
if (rpnStack.Count == 0)
{
throw new Exception("Unbalanced parenthesis");
}
}
if (rpnStack.Count == 0)
{
throw new Exception("Unbalanced parenthesis");
}
rpnStack.Pop(); // discard open parenthesis
}
else if (operators.Contains(token))
{ // Push operand to the rpn stack after moving to output all higher or equal priority operators
while (rpnStack.Count > 0 && ((string)rpnStack.Peek()).Equals("AND"))
{
PostfixTokens.Add(rpnStack.Pop()); // Pop and add to output
}
rpnStack.Push(token); // Now put the operator onto the stack
}
else
{
throw new Exception("Unrecognised token " + token);
}
}
// Copy what's left on the rpnStack
while (rpnStack.Count > 0)
{ // move to the output all remaining operators
if (((string)rpnStack.Peek()).Equals("("))
{
throw new Exception("Unbalanced parenthesis");
}
PostfixTokens.Add(rpnStack.Pop());
}
}
