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));
}
}