逆波兰式求解多项式

蔚落 2022-05-23 00:09 180阅读 0赞

![这里写图片描述][70]

import java.util.Stack;
    public class Solution {
        //逆波兰式求解多项式计算
        public int evalRPN(String[] tokens) {
            if(tokens==null)
                return 0;
            if(tokens.length==1&&tokens[0]!="+"
              &&tokens[0]!="-"&&tokens[0]!="*"&&tokens[0]!="/")
             return Integer.parseInt(tokens[0]);
            Stack<Integer>stack=new Stack<Integer>();
            stack.push(Integer.parseInt(tokens[0]));
            stack.push(Integer.parseInt(tokens[1]));
            int temp1=0;
            int temp2=0;
            for(int i=2;i!=tokens.length;i++)
            {
                if(tokens[i].equals("+"))
                {
                   temp1=stack.pop();
                   temp2=stack.pop();
                   stack.push(temp1+temp2);
                }else if(tokens[i].equals("-"))
                {
                   temp1=stack.pop();
                   temp2=stack.pop();
                   stack.push(temp2-temp1);
    
                }else if(tokens[i].equals("*"))
                {
                   temp1=stack.pop();
                   temp2=stack.pop();
    
                   stack.push(temp1*temp2);
                }else if(tokens[i].equals("/"))
                {
                   temp1=stack.pop();
                   temp2=stack.pop();
                   if(temp1==0||temp2==0)
                   {
                       stack.push(0);
                   }else{
                     stack.push(temp2/temp1);
                   }
    
                }else{
    
                   stack.push(Integer.parseInt(tokens[i]));
                }
            }
            return stack.pop();
    
        }
    
        //方法二:运用try-catch计算公式
        public int evalRPN2(String[] tokens) {
           if(tokens==null)
                return 0;
            if(tokens.length==1&&tokens[0]!="+"
              &&tokens[0]!="-"&&tokens[0]!="*"&&tokens[0]!="/")
             return Integer.parseInt(tokens[0]);
    
            Stack<Integer>stack=new Stack<Integer>();
            int a=0;
            int b=0;
            for(int i=0;i!=tokens.length;i++)
            {
              try{
                stack.add(Integer.parseInt(tokens[i]));
    
               }catch(Exception e){
                b=stack.pop();
                a=stack.pop();
                stack.push(compute(a,b,tokens[i]));
               }
            }
            return stack.pop();
        }
    
        public int compute(int a,int b,String operator)
        {
            switch (operator) 
            {
                case "+":
                    return a+b;
                case "-":
                    return a-b;
                case "*":
                    return a*b;
                case "/":
                    return a/b;
                default:
                    return 0;
    
            }
    
        }
    
        public static void main(String[]args){
             //System.out.println("Hello");
            //String[]tokens={"2","1","+","3","*"};
            String[]tokens={
       "4","3","-"};
            Solution s=new Solution();
            System.out.println(s.evalRPN2(tokens));
    
        }
    }

![这里写图片描述][70 1]

[70]: /images/20220523/31d4eafc8f7946029e3f22c832f19a70.png
[70 1]: /images/20220523/f4b3f7adfafa497e8a3d71b146d2033f.png