1#include <stdio.h>
 2#include <stdlib.h>
 3
 4int collatz(int a) {
 5    if (a % 2 == 0)
 6        return a / 2;
 7    return 3 * a + 1;
 8}
 9
10void collatzSequence(char *buf, int a) {
11    int offset = sprintf(buf, "%d: ", a);
12    for (int i = a; i >= 1; i = collatz(i)) {
13        if (i == 1) {
14            sprintf(buf + offset, "1");
15            break;
16        }
17        offset += sprintf(buf + offset, "%d, ", i);
18    }
19}
20
21int main(void) {
22    char *buf = malloc(sizeof(char) * 8192);
23    for (int i = 1; i <= 10000; i++) {
24        collatzSequence(buf, i);
25        if (buf == NULL) {
26            fprintf(stderr, "memory allocation failed");
27            return 1;
28        }
29        puts(buf);
30    }
31    free(buf);
32    return 0;
33}