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：
 1 public class Solution {
 2     public int evalRPN(String[] s) {
 3         
 4        Stack<Integer> stack1=new Stack<>();
 5         for(int i=0;i<s.length;i++)
 6         {
 7             if(s[i].equals("+"))
 8                 {
 9                 int a=stack1.pop();
10                 int b=stack1.pop();
11                 stack1.push(a+b);
12                 }
13             else if(s[i].equals("-"))
14             {
15             int a=stack1.pop();
16             int b=stack1.pop();
17             stack1.push(b-a);
18             }
19             else if(s[i].equals("*"))
20             {
21             int a=stack1.pop();
22             int b=stack1.pop();
23             stack1.push(a*b);
24             }
25             else if(s[i].equals("/"))
26             {
27             int a=stack1.pop();
28             int b=stack1.pop(); 
29             stack1.push(b/a);
30             }
31             else
32             {
33                 try{stack1.push(Integer.parseInt(s[i].trim()));}
34             catch(NumberFormatException e){}
35                 
36             }
37                 
38         }
39         return stack1.peek();
40     }
41 }