LeetCode-Evaluate Reverse Polish Notation[AC源码]

 package com.lw.leet2;

 /**
  * @ClassName:Solution
  * @Description:
  *         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
  *
  * @Author LiuWei
  * @Date 2014年8月16日上午11:31:05
  * @Mail nashiyue1314@163.com
  */
 public class Solution {

     private boolean isOper(String s){
         if(s.equals("+")){
             return true;
         }
         if(s.equals("-")){
             return true;
         }
         if(s.equals("*")){
             return true;
         }
         if(s.equals("/")){
             return true;
         }
         return false;
     }

     private String getOperRes(String num1,String num2,String oper){
         if(oper.equals("+")){
             return Integer.valueOf(num1)+Integer.valueOf(num2)+"";
         }
         else if(oper.equals("-")){
             return Integer.valueOf(num1)-Integer.valueOf(num2)+"";
         }
         else if(oper.equals("*")){
             return Integer.valueOf(num1)*Integer.valueOf(num2)+"";
         }
         else{
             return Integer.valueOf(num1)/Integer.valueOf(num2)+"";
         }
     }

     public int evalRPN(String[] tokens) {
         String[] resArr = new String[tokens.length];
         int index =0;
         for(int i=0;i<tokens.length;i++){
             if(isOper(tokens[i])){
                 String num1 = resArr[index-1];
                 String num2 = resArr[index-2];
                 resArr[index-2] = getOperRes(num2, num1, tokens[i]);
                 index--;
             }
             else{
                 resArr[index] = tokens[i];
                 index ++;
             }
         }
         return Integer.valueOf(resArr[0]);
     }

     public static void main(String[] args){
         Solution s = new Solution();
 //        String [] tokens = {"4", "13", "5", "/", "+"};
         String [] tokens = {"2", "1", "+"};
         System.out.println(s.evalRPN(tokens));
     }
 }