算法Sedgewick第四版-第1章基础-013一用stack实现自动补全表达式括号

 package algorithms.exercise;

 import algorithms.ADT.Stack;
 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 /*************************************************************************
  *
  *  % java Ex_1_3_09
  *  1 + 2 ) * 3 - 4 ) * 5 - 6 ) ) )
  *  ( ( 1 + 2 ) * ( ( 3 - 4 ) * ( 5 - 6 ) ) )
  *
  *  % java Ex_1_3_09
  *  sqrt 1 + 2 ) )
  *  ( sqrt ( 1 + 2 ) )
  *
  *************************************************************************/

 public class Ex_1_3_09
 {
     public static void main(String[] args)
     {
         Stack<String> ops  = new Stack<String>();
         Stack<String> vals = new Stack<String>();

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

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

                 if (op.equals("+") ||
                     op.equals("-") ||
                     op.equals("*") ||
                     op.equals("/"))
                     v = String.format("( %s %s %s )", vals.pop(), op, v);
                 else if (op.equals("sqrt"))
                     v = String.format("( %s %s )", op, v);

                 vals.push(v);
             }
             else vals.push(s);
             //else vals.push(((Double)Double.parseDouble(s)).toString());
         }

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