题解 | 逆波兰表达式求值

import java.util.*;


public class Solution {
    public int evalRPN (String[] tokens) {
        // write code here
        Stack<Integer> stack = new Stack<>();
	  	// 注意这里是要把每次的结果也一起压入栈中，继续计算
        for(String token : tokens){
            if(!token.equals("+") && !token.equals("-") && !token.equals("*") && !token.equals("/")){
                stack.push(Integer.parseInt(token));
            }else{
                int num1 = stack.pop();
                int num2 = stack.pop();
                if(token.equals("+")){
                    stack.push(num1 + num2);
                }else if(token.equals("-")){
                    stack.push(num2 - num1);
                }else if(token.equals("*")){
                    stack.push(num2 * num1);
                }else if(token.equals("/")){
                    stack.push(num2 / num1);
                }
            }
        }
        return stack.pop();
    }
}