#include <stdio.h>
#include <stdlib.h>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
#define NUM 4

enum abcd{D,A,C,B};
enum Y_N{NO,YES};

void choice(enum abcd);
void mydisplay(const int []);
enum Y_N isrational(int,const int[],enum abcd);
 
int main(void) 
{
	choice(D);
	
	return 0;
}

void choice(enum abcd choicing)
{
	static int choiced[NUM];
	int i;
	
	if(choicing>B)
	{
		printf("找到符合要求的數:");
		mydisplay(choiced);
		return;
	}
	
	for(i=0;i<=9;i++)
	{
		if(isrational(i,choiced,choicing)==YES)
		{
			choiced[choicing]=i;
			choiced[choicing]=i;
			choice(choicing+1); 
		}
	}
	return;
}

void mydisplay(const int choiced[])
{
	printf("%d%d%d%d",choiced[A],choiced[B],choiced[C],choiced[D]);
	printf("\n");
}

enum Y_N isrational(int i,const int choiced[],enum abcd choicing)
{
	switch(choicing)
	{
		case D:return (i!=0)?YES:NO;
		case A:return (i!=0&&(choiced[D]*9)%10==i
						   &&i*9<=9)?YES:NO;
		case C:return YES;
		case B:return (choiced[D]*9+choiced[C]*90+i*900+choiced[A]*9000==
		             choiced[A]+i*10+choiced[C]*100+choiced[D]*1000)?YES:NO;
	}
}