package com.coding.basic.stack.myself;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
import com.coding.basic.stack.myself.Token;
public class PrefixExpr {
String expr = null;
public PrefixExpr(String expr) {
this.expr = expr;
}
public float evaluate() {
TokenParser parser = new TokenParser();
List<Token> tokens = parser.parse(expr);
Stack<Token> exprStack = new Stack<>();
Stack<Float> numStack = new Stack<>();
for(Token token : tokens){
exprStack.push(token);
}
while(!exprStack.isEmpty()){
Token t = exprStack.pop();
if(t.isNumber()){
numStack.push(new Float(t.getIntValue()));
}else{
Float f1 = numStack.pop();
Float f2 = numStack.pop();
numStack.push(calculate(t.toString(),f1,f2));
}
}
return numStack.pop().floatValue();
}
public float calculate(String op, float f1, float f2){
if(op.equals("+")){
return f1+f2;
}
if(op.equals("-")){
return f1-f2;
}
if(op.equals("*")){
return f1*f2;
}
if(op.equals("/")){
return f1/f2;
}
throw new RuntimeException(op + " is not supported");
}
}