技術標籤：演算法演算法資料結構stack

本系列部落格源自學習《尚矽谷資料結構與演算法》的學習隨筆。

package test.learn.algorithm.PolandNotation;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class poland {
    public static void main(String[] args) {
        String expression = "4 5 * 8 - 60 + 8 2 / +"
 
;
        List<String> list = getList(expression);
        System.out.println(list);
        System.out.println(calculate(list));
    }
    //將逆波蘭式傳入一個數組之中
    public static List<String> getList(String express){
        String [] spilt = express.split(" ");
        List<String>
 
 list = new ArrayList<String>();
        for (String s : spilt) {
            list.add(s);
        }
        //System.out.println(list);
        return list;
    }
    //完成對逆波蘭式的掃描
    public static int calculate(List<String> list){
        Stack<String> stack = new Stack<String>
 
();
        for (String l : list) {
            if(l.matches("\\d+")){
                stack.push(l);
            }else{
                //彈出兩個數
                int num1 = Integer.parseInt(stack.pop());
                int num2 = Integer.parseInt(stack.pop());
                int res = 0;
                switch (l){
                    case"+":
                        res = num1+num2;
                        break;
                    case"-":
                        res = num2-num1;
                        break;
                    case"/":
                        res =num2/num1;
                        break;
                    case"*":
                        res =num1*num2;
                        break;
                    default:
                        break;
                }
                stack.push(""+res);
            }
        }
        return Integer.parseInt(stack.pop());
    }
}