练习题 逆波兰表达式求值

逆波兰表达式求值
逆波兰表达式求值

后缀表达式也叫逆波兰表达式

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack=new Stack<>();
        for(String s:tokens){
            if(!isOperation(s)){
                stack.push(Integer.parseInt(s));
            }else{
                int num2=stack.pop();
                int num1=stack.pop();
                switch(s){
                    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();
    }
    public boolean isOperation(String s){
        if(s.equals("+")||s.equals("-")||s.equals("*")||s.equals("/"))
            return true;
        return false;
    }
}