150. Evaluate Reverse Polish Notation

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
代码如下：

 public class Solution {
     public int evalRPN(String[] s) {

        Stack<Integer> stack1=new Stack<>();
         for(int i=0;i<s.length;i++)
         {
             if(s[i].equals("+"))
                 {
                 int a=stack1.pop();
                 int b=stack1.pop();
                 stack1.push(a+b);
                 }
             else if(s[i].equals("-"))
             {
             int a=stack1.pop();
             int b=stack1.pop();
             stack1.push(b-a);
             }
             else if(s[i].equals("*"))
             {
             int a=stack1.pop();
             int b=stack1.pop();
             stack1.push(a*b);
             }
             else if(s[i].equals("/"))
             {
             int a=stack1.pop();
             int b=stack1.pop();
             stack1.push(b/a);
             }
             else
             {
                 try{stack1.push(Integer.parseInt(s[i].trim()));}
             catch(NumberFormatException e){}

             }

         }
         return stack1.peek();
     }
 }