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/**
* Histogram sort
*
* This sort is interesting in that it is a "comparison-free" sort. That is to
* say that it doesn't ever directly compare two items against each other to
* determine the larger one, much like conventional sorting algorithms does.
*
* Instead, a histogram is built by counting the frequency of each value in
* the input set. Then, a sorted output set is constructed from this histogram
* since it is implicitly in order.
*
* This has the disadvantage of becoming heavy on memory usage when the input
* values increase in range. Theoretically, if the range was high, but sparse,
* some simple compression could be applied. There's an area for
* experimentation.
*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define RANGE 10000
#define COUNT 10000000
int is_sorted(unsigned int *data, size_t length)
{
size_t i = 0;
for (i = 0; i < length-1; i++)
if (data[i] > data[i+1])
return 0;
return 1;
}
void fill_random(unsigned int *data, size_t length, unsigned int max)
{
size_t i = 0;
for (i = 0; i < length; i++)
data[i] = rand()%max+1;
}
void sort(unsigned int *data, size_t length, unsigned int max)
{
size_t *hist = calloc(max+1, sizeof(size_t));
size_t i = 0;
size_t j = 0;
for (i = 0; i < length; i++) {
hist[data[i]]++;
}
j = 0;
for (i = 0; i < max+1; i++) {
for (; hist[i]; hist[i]--, j++)
data[j] = i;
}
}
void dump_data(unsigned int *data, size_t length)
{
size_t i = 0;
for (i = 0; i < length; i++)
printf("%d, ", data[i]);
fputc('\n', stdout);
}
int main(int argc, char **argv)
{
unsigned int *data = calloc(COUNT, sizeof(unsigned int));
if (!data) {
perror("calloc");
return 1;
}
srand(time(NULL));
fill_random(data, COUNT, RANGE);
//dump_data(data, COUNT);
sort(data, COUNT, RANGE);
//dump_data(data, COUNT);
if (!is_sorted(data, COUNT)) {
fprintf(stderr, "Failed: out of order\n");
} else {
printf("Success.\n");
}
}
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