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

#define MAX_NUM 9999

typedef struct Node {
	int data;
	struct Node* next;
} Node;


Node* create(int data, Node* node)
{
	Node* new = (Node*)malloc(sizeof(Node));
	if (new == NULL) {
		printf("Error allocating memory\n");
		exit(1);
	}

	new->data = data;
	new->next = node;
	return new;
}


Node* prepend(Node* head, int data)
{
	return create(data, head);
}


int contains(Node* head, int data)
{
	Node* cursor = head;

	while (cursor != NULL) {
		if (cursor->data == data)
			return 1;
		cursor = cursor->next;
	}

	return 0;
}


int sum(Node* head)
{
	int total = 0;
	Node* cursor = head;

	while (cursor != NULL) {
		total += cursor->data;
		cursor = cursor->next;
	}

	return total;
}


int countDigits(long num)
{
	int count = 0;

	while (num != 0) {
		count++;
		num /= 10;
	}

	return count;
}


int isNineDigits(int i, int j)
{
	return 9 == countDigits(i) + countDigits(j) + countDigits(i*j);
}


int isNinePandigital(int i, int j)
{
	int rem;
	int digits = 0;
	int prod = i*j;

	if (!(isNineDigits(i, j)))
		return 0;

	while (i>0) {
		rem = i % 10;
		digits ^= 1 << rem;
		i /= 10;
	}

	while (j>0) {
		rem = j % 10;
		digits ^= 1 << rem;
		j /= 10;
	}

	while (prod>0) {
		rem = prod % 10;
		digits ^= 1 << rem;
		prod /= 10;
	}

	return digits == 1022; /* 1022 == 1111111110 in binary */
}


int main(int argc, char** argv)
{
	int i, j;
	int sumProds;
	Node* pandigitals = NULL;

	for (i=1; i<MAX_NUM; i++)
		for (j=1; j<MAX_NUM; j++)
			if (isNinePandigital(i, j) && !contains(pandigitals, i*j))
				pandigitals = prepend(pandigitals, i*j);

	sumProds = sum(pandigitals);
	printf("The sum of the nine pandigital products is %d\n", sumProds);
	return 0;
}