tasks a-s

Task/Parsing-RPN-calculator-algorithm/Java/parsing-rpn-calculator-algorithm.java

@@ -0,0 +1,59 @@
+import java.util.LinkedList;
+
+public class RPN{
+	public static void evalRPN(String expr){
+		String cleanExpr = cleanExpr(expr);
+		LinkedList<Double> stack = new LinkedList<Double>();
+		System.out.println("Input\tOperation\tStack after");
+		for(String token:cleanExpr.split("\\s")){
+			System.out.print(token+"\t");
+			Double tokenNum = null;
+			try{
+				tokenNum = Double.parseDouble(token);
+			}catch(NumberFormatException e){}
+			if(tokenNum != null){
+				System.out.print("Push\t\t");
+				stack.push(Double.parseDouble(token+""));
+			}else if(token.equals("*")){
+				System.out.print("Operate\t\t");
+				double secondOperand = stack.pop();
+				double firstOperand = stack.pop();
+				stack.push(firstOperand * secondOperand);
+			}else if(token.equals("/")){
+				System.out.print("Operate\t\t");
+				double secondOperand = stack.pop();
+				double firstOperand = stack.pop();
+				stack.push(firstOperand / secondOperand);
+			}else if(token.equals("-")){
+				System.out.print("Operate\t\t");
+				double secondOperand = stack.pop();
+				double firstOperand = stack.pop();
+				stack.push(firstOperand - secondOperand);
+			}else if(token.equals("+")){
+				System.out.print("Operate\t\t");
+				double secondOperand = stack.pop();
+				double firstOperand = stack.pop();
+				stack.push(firstOperand + secondOperand);
+			}else if(token.equals("^")){
+				System.out.print("Operate\t\t");
+				double secondOperand = stack.pop();
+				double firstOperand = stack.pop();
+				stack.push(Math.pow(firstOperand, secondOperand));
+			}else{//just in case
+				System.out.println("Error");
+				return;
+			}
+			System.out.println(stack);
+		}
+		System.out.println("Final answer: " + stack.pop());
+	}
+	
+	private static String cleanExpr(String expr){
+		//remove all non-operators, non-whitespace, and non digit chars
+		return expr.replaceAll("[^\\^\\*\\+\\-\\d/\\s]", "");
+	}
+	
+	public static void main(String[] args){
+		evalRPN("3 4 2 * 1 5 - 2 3 ^ ^ / +");
+	}
+}