【LeetCode刷题-栈】-- 150.逆波兰表达式求值

150.逆波兰表达式求值

方法：使用栈

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> numStack = new Stack<>();
        for(int i = 0; i < tokens.length;i++){
            String token = tokens[i];
            if(isNumber(token)){
                numStack.push(Integer.parseInt(token));
            }else{
                int num1 = numStack.pop();
                int num2 = numStack.pop();
                switch(token){
                    case "+":
                        numStack.push(num1 + num2);
                        break;
                    case "-":
                        numStack.push(num2 - num1);
                        break;
                    case "*":
                        numStack.push(num1 * num2);
                        break;
                    case "/":
                        numStack.push(num2 / num1);
                        break;
                    default:
                }
           
            }
        }
        return numStack.pop();
    }
    public boolean isNumber(String token){
        return !("+".equals(token) || "-".equals(token) || "*".equals(token) || "/".equals(token));
    }
}