public static BinaryNode Parse(string input)
{
BinaryNode root = null;
BinaryNode current = null;
BinaryNode parent = null;
// opStack holds the method/function (add/sub/div/mult)
// while the input is being parsed
Stack <string> opStack = new Stack <string>();
// valueStack holds the integers while the
// input is being parsed
Stack <string> valueStack = new Stack <string>();
// nodes holds the BinaryNodes, so when a
// parent node needs to be assigned, it somes
// from here
List <BinaryNode> nodes = new List <BinaryNode>();
// keep track of the depth level in the tree
int level = 0;
int index = 0;
foreach (char token in input.ToCharArray())
{
if (token == '(') // if we get here when parsing, the opStack should now have the method/function
{
// get the method from opStack could be add/sub/mult/div at this time
string method = FromStack(opStack);
if (root == null)
{
root = new BinaryNode(GetMethod(method));
current = root;
parent = root;
nodes.Add(root);
}
else
{
// keep track of the parent node
parent = current;
current = new BinaryNode(GetMethod(method));
if (parent.LeftNode == null)
{
parent.LeftNode = current;
}
else
{
parent.RightNode = current;
}
nodes.Add(current);
level++;
index++;
}
// clear the opStack
opStack.Clear();
}
// at close parens, we can create a leaf node (ValueNode)
// it also means we are done parsin an expression,
// the parser will continue at a diff depth/level
if (token == ')')
{
if (current.RightNode == null)
{
string value = FromStack(valueStack);
current.RightNode = new ValueNode(Int32.Parse(value));
valueStack.Clear();
}
// checking for level value here,
// at the end of an expression, there can be multiple left perens,
// they were causing an issue here
if (level > 0)
{
level--;
current = nodes[level];
}
}
// if we get to a comma, we should know the value for the leaf node (ValueNode)
if (token == ',')
{
if (current.LeftNode == null)
{
string value = FromStack(valueStack);
current.LeftNode = new ValueNode(ParseInteger(value));
valueStack.Clear();
}
}
// push numbers on the valueStack
if (token >= 48 && token <= 57)
{
valueStack.Push(token.ToString());
}
// push letters on the opStack
// whether is a valid method/function,
// it will checked later
if (token >= 97 && token <= 122)
{
opStack.Push(token.ToString());
}
}
return(root);
}
