栈的应用场景(一)

1.题目

2.思路

3.代码

class Solution {
    public int evalRPN(String[] tokens) {
        //创建一个栈
        Stack<Integer> stack = new Stack<>();
        //对字符串数组进行遍历
        for(String x : tokens){
            //分数操作符和操作数两种情况,我们得判断
            //一下字符串是操作数还是操作符
            //如果是数字
            if(!isOperation(x)){
                stack.push(Integer.parseInt(x));
            }
            else{
                //先右操作数,后左操作数
                 int num2 = stack.pop();
                 int num1 = stack.pop();
                 switch(x){
                     case "+":
                     stack.push(num1+num2);
                     break;
                     case "-":
                     stack.push(num1-num2);
                     break;
                     case "*":
                     stack.push(num1*num2);
                     break;
                     case "/":
                     stack.push(num1/num2);
                     break;
                 }
            }
        }
        return stack.pop();
    }
    private boolean isOperation(String x){
    if(x.equals("+")||x.equals("-")||x.equals("*")||x.equals("/")){
        return true;
    }
    return false;
    }
}