MSUBSTR spoj problem

msubstr.c

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

#define MAX_LEN 3000
#define AUX_LEN (MAX_LEN * 2 + 1)

int fn[AUX_LEN];
char aux[AUX_LEN+1];
int p[AUX_LEN];
char s[MAX_LEN+1];

/*
 * Uses manacher's algorithm
 */

static int
min(int a, int b)
{
	return a < b ? a : b;
}

static int
manacher(const char *s)
{
	const size_t slen = strlen(s);
	const size_t aux_len = slen * 2 + 2;
	int max = 0;

	aux[0] = '\xff';

	for (int i = 1, j = 0; i < aux_len; ++j, i += 2) {
		aux[i] = s[j];
		aux[i+1] = '\xff';
	}

	aux[aux_len-1] = '\0';
	memset(p, 0, aux_len * sizeof(int));
	memset(fn, 0, aux_len  * sizeof(int));

	int c = 0, r = 0, len;

	for (int i = 1; i < aux_len-1; ++i) {
		const int i_ = 2*c-i;

		len = r > i ? min(r-i, p[i_]) : 0;

		while ((i+1+len) < aux_len && (i-1-len) >= 0 && aux[i+1+len] == aux[i-1-len])
			++len;

		fn[len]++;

		if (len > max)
			max = len;

		p[i] = len;

		if (i + len > r) {
			c = i;
			r = i + len;
		}
	}

	return max;
}

int
main(void)
{
	int len;
	char s[4000];
	int m;
	scanf("%d\n", &len);

	while (len--) {
		gets(s);
		m = manacher(s);
		printf("%d %d\n", m, fn[m]);
	}

	return 0;
}