leetcode--Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in 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

[java] view plain copy

1. public class Solution {  
2.     public int evalRPN(String[] tokens) {  
3.         Stack<String> stack = new Stack<String>();        
4.         int num1 = 0;  
5.         int num2 = 0;  
6.         for(int i=0;i<tokens.length;i++){  
7.             switch (tokens[i]) {  
8.             case "+":  
9.                 num1 = Integer.valueOf(stack.pop());  
10.                 num2 = Integer.valueOf(stack.pop());  
11.                 stack.add((num2+num1)+"");  
12.                 break;  
13.             case "-":  
14.                 num1 = Integer.valueOf(stack.pop());  
15.                 num2 = Integer.valueOf(stack.pop());  
16.                 stack.add((num2-num1)+"");  
17.                 break;  
18.             case "*":  
19.                 num1 = Integer.valueOf(stack.pop());  
20.                 num2 = Integer.valueOf(stack.pop());  
21.                 stack.add((num2*num1)+"");  
22.                 break;  
23.             case "/":  
24.                 num1 = Integer.valueOf(stack.pop());  
25.                 num2 = Integer.valueOf(stack.pop());  
26.                 stack.add((num2/num1)+"");  
27.                 break;  
28.             default:  
29.                 stack.add(tokens[i]);  
30.                 break;  
31.             }  
32.         }  
33.         return Integer.valueOf(stack.pop());  
34.     }  
35. }  

原文链接http://blog.csdn.net/crazy__chen/article/details/46566389