public static Double eval(LinkedList<MyNode> postfixExp) {
Stack theStack = new Stack();
Double temp;
Double newVal = 0.0;
Double under;
char op;
String evaluate;
MyNode thisNode;
for (MyNode t : postfixExp) {
thisNode = t;
if (thisNode.getOp() == '0') theStack.push(thisNode.getValue());
else {
// want to check if r/l/s, if thats the case, just pull top, apply operator, push
if (thisNode.getOp() == 'r' || thisNode.getOp() == 'l' || thisNode.getOp() == 's') {
op = thisNode.getOp();
temp = (Double) theStack.pop();
switch (op) {
case 'l':
newVal = Math.log(temp);
break;
case 'r':
newVal = (Double) (1 / temp);
break;
case 's':
newVal = Math.sqrt(temp);
break;
}
theStack.push(newVal);
} else {
temp = (Double) theStack.pop();
under = (Double) theStack.pop();
op = thisNode.getOp();
switch (op) {
case '+':
newVal = under + temp;
break;
case '-':
newVal = under - temp;
break;
case '/':
newVal = under / temp;
break;
case '*':
newVal = under * temp;
break;
case '^':
newVal = Math.pow(under, temp);
break;
default:
break;
}
theStack.push(newVal);
}
}
}
Double toReturn = (Double) theStack.pop();
return toReturn;
}
public static LinkedList<MyNode> convert(LinkedList<MyNode> inFixExp) {
LinkedList<MyNode> toReturn = new LinkedList<MyNode>();
MyNode thisNode;
MyNode topOperator;
Stack theStack = new Stack();
for (MyNode t : inFixExp) {
thisNode = t;
if (thisNode.getOp() == '0') // Node is a double
toReturn.add(thisNode);
else { // Node is an operator
if (thisNode.getOp() == '(') theStack.push(thisNode);
else if (thisNode.getOp() == ')') { // Node is right parens
while (((MyNode) theStack.peek()).getOp() != '(') {
toReturn.add((MyNode) theStack.pop());
}
theStack.pop();
} else if (theStack.empty()) theStack.push(thisNode);
else {
topOperator = (MyNode) theStack.peek();
if (hasPrecedence(
thisNode.getOp(),
topOperator.getOp())) { // operator has precedence over top operator of stack
theStack.push(thisNode);
} else { // operator does not have precedence over top operator of stack
toReturn.add((MyNode) theStack.pop());
theStack.push(thisNode);
}
}
}
}
// all items have been seen
while (!theStack.empty()) {
toReturn.add((MyNode) theStack.pop());
}
return toReturn;
}
