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  • evaluate-reverse-polish-notation

    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

    这里采用别人使用异常来做判断,这个我个人觉得很厉害。

    public int evalRPN(String[] tokens){
            Stack<Integer> stack = new Stack<Integer>();
            for(int i = 0; i<tokens.length;i++){
                try{
                    int num = Integer.parseInt(tokens[i]);
                    stack.add(num);
                }catch(Exception e){
                    int b = stack.pop();
                    int a = stack.pop();
                    stack.add(get(a,b,tokens[i]));
                }
                
            }
            return stack.pop();
        }
        private int get(int a, int b,String op){
            switch(op){
            case "+":
                return a + b;
            case "-":
                return a - b;
            case "*":
                return a * b;
            case "/":
                return a / b;
            default:
                return 0;
            }
                    
        }
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  • 原文地址:https://www.cnblogs.com/LoganChen/p/8086089.html
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