Question

Solution

2 1 + 3 *是((2+1)*3)的后缀(postfix)或逆波兰(reverse Polish)记法，计算这个表达式容易想到栈，当见到一个数时就入栈，见到操作符时该运算符作用于从该栈中弹出的两个数上，将所得结果入栈。

public int evalRPN(String[] tokens) {    Stack
    
      stack = new Stack<>();    for (String tmp : tokens) {        if (tmp.length() > 1) {            stack.push(Integer.parseInt(tmp));            continue;        }        char c = tmp.charAt(0); // String转char        int a, b;        switch (c) {            case '+':                b = stack.pop();                a = stack.pop();                stack.push(a + b);                break;            case '-':                b = stack.pop();                a = stack.pop();                stack.push(a - b);                break;            case '*':                b = stack.pop();                a = stack.pop();                stack.push(a * b);                break;            case '/':                b = stack.pop();                a = stack.pop();                stack.push(a / b);                break;            default:                stack.push(c - '0'); // char 转 int        }    }    return stack.pop();}
    

Reference