2006程式設計競賽第四題

題目：

Factoring a number means representing it as the product of prime numbers. 

Please write a program to factoring a number. 

程式碼：

import java.util.*;

/*********************************************
 * Factoring a number means representing it as
 * the product of prime numbers. Please write a
 * program to factoring a number. 
 *********************************************/

public class E2006_4{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt();//輸入整數
            System.out.println("Please input a number: "+ n);           
            List<Integer> list = new ArrayList<Integer>();
            prime(list);
            facNum(list,n);

            
        }    
    }


    public static void prime(List<Integer> list){
            /*找前100質數放入容器 */
            int i,c=0;
            for(i=2; i<=100; i++){//質數的定義來寫
                for(int j=2; j<=i; j++){
                    if(i%j==0){ 
                        c++;    
                    }
                }
                if(c==1){
                    list.add(i);//存取元素至清單
                }
                c = 0;
            }
            /*印出 list 存放元素 */
            //for(Integer num : list){ System.out.println(num); }
            //System.out.print(list.size());//容器存放多少個元素
    }
    /*找出相鄰質數相乘 == 輸入的數字 */
    public static void  facNum(List<Integer> list,int num){
         for(int j = 0 ; j < list.size() - 1 ; j ++){
            if(list.get(j) * list.get(j + 1) == num){
                System.out.println(num+" is product by : "+list.get(j) + "," + list.get(j+1));
                break ; 
            }
            else if(list.get(j) * list.get(j+1) > num){
                break ; 
            }
        }
         
    }

}

Ex.

Please input a number: 221
221 is product by : 13, 17
Please input a number: 77
77 is product by : 7, 11 

心得：

list 是朋友教我的，感覺不錯用。困難點是 list 的用法吧!!只能在最近多學。也希望讀者有更好的方式來解答此題，答案給的不足，明確度應該不高ㄅQQ