PAT/PATAdvanced/1023.c

#include <stdio.h>
#include <string.h>

void reverse(char n[])
{
	char temp;
	int len = strlen(n);
	for (int i = 0; i < len / 2; i++) {
		temp = n[i];
		n[i] = n[len - i - 1];
		n[len - i - 1] = temp;
	}
}

void doubleLargeNumber(char n[], char n2[])
{
	int l, s = 0, len = strlen(n);

	for (int i = 0; i < len; i++) {
		s += 2 * (n[i] - '0');
		l = s / 10;
		s %= 10;
		n2[i] = s + '0';

		s = l;
	}

	if (s)
		n2[len] = s + '0';
}

int main()
{
	char N[22] = {0}, N2[22] = {0};
	int diffcount[10] = {0};

	scanf("%s", N);
	/* store number in reverse order */
	reverse(N);
	doubleLargeNumber(N, N2);
	/* reverse back (just need N2) for printing */
	reverse(N2);

	/* Count the difference of counts of digits 0-9 */
	for (int i = 0; i < strlen(N); i++)
		diffcount[N[i] - '0']++;
	for (int i = 0; i < strlen(N2); i++)
		diffcount[N2[i] - '0']--;

	/* Check */
	for (int i = 0; i < 10; i++)
		if (diffcount[i]) {
			printf("No\n%s", N2);
			return 0;
		}
	printf("Yes\n%s", N2);

	return 0;
}