LeetCode:Evaluate Reverse Polish Notation

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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

只处理加减乘除，没有括号，遇到数字就压栈，遇到符号就从栈中弹出2个数字进行相应计算，并将结果压栈，结束后从栈中弹出结果。

public class Solution {    public int evalRPN(String[] tokens) {        int len=tokens.length;        Stack<Integer> stack=new Stack<Integer>();        int num1,num2;        for(int i=0;i<len;i++)        {            if(tokens[i].equals("+"))            {                num2=stack.pop();                num1=stack.pop();                stack.add(num1+num2);                continue;            }            if(tokens[i].equals("-"))            {                num2=stack.pop();                num1=stack.pop();                stack.add(num1-num2);                continue;            }            if(tokens[i].equals("*"))            {                num2=stack.pop();                num1=stack.pop();                stack.add(num1*num2);                continue;            }                 if(tokens[i].equals("/"))            {                num2=stack.pop();                num1=stack.pop();                stack.add(num1/num2);                continue;            }                        stack.add(Integer.valueOf(tokens[i]));                    }        return stack.pop();    }}

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