题解 | #逆波兰表达式求值#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param tokens string字符串一维数组 
     * @return int整型
     */
    public int evalRPN (String[] tokens) {
        // write code here
        int i =0;
        Stack<Integer>stack = new Stack<>();
        while(i<tokens.length){
            String c = tokens[i];
            i++;
            switch(c){
                case "+":
                    stack.push(stack.pop()+stack.pop());
                    break;
                case "-":
                    stack.push(stack.pop()*(-1)+stack.pop());
                    break;
                case "*":
                    stack.push(stack.pop()*stack.pop());
                    break;
                case "/":
                    int d= stack.pop();
                    stack.push(stack.pop()/d);
                    break;
                default:
                    stack.push(Integer.parseInt(c));

            }
        }
        return stack.peek();
	}
}