Evaluate.java

package edu.princeton.cs.algs4.ch13;

import edu.princeton.cs.introcs.StdIn;
import edu.princeton.cs.introcs.StdOut;

/**
 * Created by zqhxuyuan on 15-3-1.
 */
public class Evaluate {

    public static void main(String[] args) {
        Stack<String> ops = new Stack<>();
        Stack<Double> vals = new Stack<>();

        while(!StdIn.isEmpty()){
            String s = StdIn.readString();

            if(s.equals("("));
            else if(s.equals("+")) ops.push(s);
            else if(s.equals("-")) ops.push(s);
            else if(s.equals("*")) ops.push(s);
            else if(s.equals("/")) ops.push(s);

            else if(s.equals(")")) {
                String op = ops.pop();
                double v = vals.pop();
                if(op.equals("+")) v = vals.pop() + v;
                else if(op.equals("-")) v = vals.pop() - v;
                else if(op.equals("*")) v = vals.pop() * v;
                else if(op.equals("/")) v = vals.pop() / v;
                else if(op.equals("sqrt")) v = Math.sqrt(v);
                vals.push(v);
            }

            else vals.push(Double.parseDouble(s));
        }

        StdOut.println(vals.pop());
    }
}