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#include <stdio.h>
char a[4];
char largest_digit(short n)
{
char m = n / 1000;
if (m < n % 1000 / 100)
m = n % 1000 / 100;
if (m < n % 100 / 10)
m = n % 100 / 10;
return (m < n % 10) ? n % 10 : m;
}
void sort_digits(short n)
{
char i, j;
a[0] = n / 1000;
a[1] = n % 1000 / 100;
a[2] = n % 100 / 10;
a[3] = n % 10;
for (i = 0; i < 3; i++)
for (j = i + 1; j < 4; j++)
if (a[i] < a[j]) {
a[i] += a[j];
a[j] = a[i] - a[j];
a[i] -= a[j];
}
}
short desc_digits(short n)
{
sort_digits(n);
return a[0] * 1000 + a[1] * 100 + a[2] * 10 + a[3];
}
unsigned long long kaprekar(short n)
{
char i;
for (i = 0; n ^ 6174; i++) {
sort_digits(n);
n = (a[0] - a[3]) * 999 + (a[1] - a[2]) * 90;
}
return i;
}
int main()
{
printf("largest_digit(1234) -> %hhd\n", largest_digit(1234));
printf("largest_digit(3253) -> %hhd\n", largest_digit(3253));
printf("largest_digit(9800) -> %hhd\n", largest_digit(9800));
printf("largest_digit(3333) -> %hhd\n", largest_digit(3333));
printf("largest_digit(120) -> %hhd\n\n", largest_digit(120));
printf("desc_digits(1234) -> %hd\n", desc_digits(1234));
printf("desc_digits(3253) -> %hd\n", desc_digits(3253));
printf("desc_digits(9800) -> %hd\n", desc_digits(9800));
printf("desc_digits(3333) -> %hd\n", desc_digits(3333));
printf("desc_digits(120) -> %hd\n\n", desc_digits(120));
printf("kaprekar(6589) -> %lld\n", kaprekar(6589));
printf("kaprekar(5455) -> %lld\n", kaprekar(5455));
printf("kaprekar(6174) -> %lld\n", kaprekar(6174));
return 0;
}
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