LeetCode题解-逆波兰表达式求值-Java

一看就懂，用的栈，表达式求值的经典套路

class Solution {
   
    public int evalRPN(String[] tokens) {
   
        Stack<Integer> numStack=new Stack<>();
        for (String token : tokens) {
   
            if (!isOperator(token)){
   
                numStack.push(Integer.parseInt(token));
            }else {
   
                numStack.push(Operation(numStack.pop(),numStack.pop(),token.charAt(0)));
            }
        }
        return numStack.pop();
    }

    private boolean isOperator(String token) {
   
        if (token.length()>1){
   
            return false;
        }
        char first=token.charAt(0);
        return first=='+'||first=='-'||first=='*'||first=='/';
    }
    private int Operation(int one,int two,char token) {
   
        switch (token){
   
            case '+':
                return one+two;
            case '-':
                return two-one;
            case '*':
                return one*two;
            case '/':
                return two/one;
        }
        return 0;
    }
}