LeetCode Evaluate Reverse Polish Notation(用栈来计算后缀表达式)

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本文介绍了一种解决逆波兰表达式求值问题的方法。利用栈数据结构处理加减乘除运算，支持整数和表达式作为操作数。示例包括了如何解析和计算简单的逆波兰表达式。

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Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

public class Solution {
    public int evalRPN(String[] tokens) {
        String operators = "+-*/";
        int result = 0;
        
        Stack<String> stack = new Stack<String>();
        
        for (String s: tokens) {
            if (!operators.contains(s)) {
                stack.push(s);
            } else {
                int b = Integer.valueOf(stack.pop());
                int a = Integer.valueOf(stack.pop());
                switch (s) {
                    case "+":
                        stack.push(String.valueOf(a + b));
                        break;
                    case "-":
                        stack.push(String.valueOf(a - b));
                        break;
                    case "*":
                        stack.push(String.valueOf(a * b));
                        break;
                    case "/":
                        stack.push(String.valueOf(a / b));
                        break;
                }
            }
        }
        
        result = Integer.valueOf(stack.pop());
        
        return result;
    }
}