60 lines
1.9 KiB
Java
60 lines
1.9 KiB
Java
import java.util.LinkedList;
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public class RPN{
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public static void evalRPN(String expr){
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String cleanExpr = cleanExpr(expr);
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LinkedList<Double> stack = new LinkedList<Double>();
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System.out.println("Input\tOperation\tStack after");
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for(String token:cleanExpr.split("\\s")){
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System.out.print(token+"\t");
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Double tokenNum = null;
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try{
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tokenNum = Double.parseDouble(token);
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}catch(NumberFormatException e){}
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if(tokenNum != null){
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System.out.print("Push\t\t");
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stack.push(Double.parseDouble(token+""));
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}else if(token.equals("*")){
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System.out.print("Operate\t\t");
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double secondOperand = stack.pop();
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double firstOperand = stack.pop();
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stack.push(firstOperand * secondOperand);
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}else if(token.equals("/")){
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System.out.print("Operate\t\t");
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double secondOperand = stack.pop();
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double firstOperand = stack.pop();
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stack.push(firstOperand / secondOperand);
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}else if(token.equals("-")){
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System.out.print("Operate\t\t");
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double secondOperand = stack.pop();
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double firstOperand = stack.pop();
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stack.push(firstOperand - secondOperand);
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}else if(token.equals("+")){
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System.out.print("Operate\t\t");
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double secondOperand = stack.pop();
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double firstOperand = stack.pop();
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stack.push(firstOperand + secondOperand);
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}else if(token.equals("^")){
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System.out.print("Operate\t\t");
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double secondOperand = stack.pop();
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double firstOperand = stack.pop();
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stack.push(Math.pow(firstOperand, secondOperand));
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}else{//just in case
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System.out.println("Error");
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return;
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}
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System.out.println(stack);
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}
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System.out.println("Final answer: " + stack.pop());
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}
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private static String cleanExpr(String expr){
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//remove all non-operators, non-whitespace, and non digit chars
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return expr.replaceAll("[^\\^\\*\\+\\-\\d/\\s]", "");
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}
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public static void main(String[] args){
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evalRPN("3 4 2 * 1 5 - 2 3 ^ ^ / +");
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}
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}
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