homework.c

/* gcc -O3 -Wall -Werror homework.c -o homework */
/* Accepts input from stdin. echo "Input String" | homework */

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

typedef unsigned char element_t;

/* Sort order doesn't really matter */
static int sort_compare(const void *_a, const void *_b) {
	element_t a, b;
	a = *(element_t *)_a;
	b = *(element_t *)_b;

	if (a == b)
		return 0;

	return (a < b) ? -1 : 1;
}

/* Replace with a sort function of your choice */
static void sort(element_t *arr, size_t number) {
	qsort(arr, number, sizeof(*arr), sort_compare);
}

#define CHUNK_COUNT	16

int main() {
	element_t c;
	element_t *arr;
	size_t i, count, repeat_count;
	
	count = 0;
	arr = NULL;

	/* Read CHUNK_COUNT elements in at a time */
	while (1) {
		size_t read;

		/* No NULL check - we got memory 'kay */
		arr = realloc(arr, (count + CHUNK_COUNT) * sizeof(*arr));
		read = fread(arr + count, sizeof(*arr), CHUNK_COUNT, stdin);
		count += read;
		if (read < CHUNK_COUNT)
			break;
	}

	printf("[*] Finished reading. Number of elements: %ld\n", count);

	/* Sort elements */
	sort(arr, count);

	printf("[*] Finished sorting\n");

	/* Step through and count - worst case O(n) */
	c = '\0';
	repeat_count = 0;
	for (i=0; i<count; i++) {
		if (arr[i] != c) {
			c = arr[i];
			repeat_count = 0;
		}
	
		if (++repeat_count > count / 2)
			break;
	}

	printf("[*] Finished counting\n");
	
	if (repeat_count > count / 2) {
		printf("[*] Element %#02x repeats more than %ld times\n",
			c, count / 2);
	} else {
		printf("[*] No element repeats more than %ld times\n",
			count / 2);
	}

	free(arr);

	return 0;
}