Mensajes

public class Desen {
   
   public static final int[][] TERMINA1 = {{1,1},{3,7},{9,9},{-1,-1}};
   public static final int[][] TERMINA3 = {{1,3},{7,9},{-1,-1}};
   public static final int[][] TERMINA7 = {{1,7},{3,9},{-1,-1}};
   public static final int[][] TERMINA9 = {{1,9},{3,3},{7,7},{-1,-1}};
   
   public static void main(String[] args) {
      principal();
   }
   
   public static void principal() {
      long n=8441081851627;
         
      String result=recursiva(n, 0, 0, 0);
         
      
      System.out.println(result==null? n + " es primo": n+ " es mulp de " + result);
      }
   

   public static String recursiva(long num, int pos, long xt, long yt) {
      
      String str=null;
      long numact=num-(xt*yt);
         
      int[][]res=(pos==0) ? primera(numpos(numact,pos)) :comprueba(numpos(numact,pos),numpos(xt,0),numpos(yt,0));      
      

         for (int i=0; i<10 && res

• >-1; i++) {
           
              long x=xt+(long)(Math.pow(10, pos)*res
  • );
                long y=yt+(long)(Math.pow(10, pos)*res[1]);
                long z=x*y;
                if (z < num && z > 0 && numpos(num-z, pos)==0)
                   str=recursiva(num, pos + 1, x, y);
                else if (z==num && x>1 && y> 1)
                      return x+" y "+y;
                if (str != null) return str;
             
             }
          return null;
       }
       
       public static int[][] primera (int x){
          switch(x) {
             case 1: return TERMINA1;
             case 3: return TERMINA3;
             case 7: return TERMINA7;
             case 9: return TERMINA9;
              };
          return TERMINA1;
          }
       
       public static int numpos (long num, int pos) {
          String sn=(num+"");
          return Integer.parseInt(sn.substring(sn.length()-pos-1, sn.length()-pos));
       }
    
       public static int[][] comprueba (int num, int x, int y) {
          int[][] resul=new int[10][2];
          int m=0,n=0;
          for (int i=0; i<10; i++)
             for (int j=0; j<10; j++) {
                if((x==-1 ? i*j : i*y+j*x)%10==num) {
                   boolean encontrado=false;
                   if (x==-1) {                  
                      for (int k=0; k<m && !encontrado; k++)
                         encontrado= (resul[k][0]==j && resul[k][1]==i);                  
                   }
                   
                   if (!encontrado) {
                      resul[m][n++]=i;
                       resul[m++][n--]=j;
                    }
                }
             }
          if(m<resul.length){
             resul[m][0]=resul[m][1]=-1;
          }
          return resul;
       }
    }