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#include "aoc.h"
#include "allocator.h"
#include "util.h"
#include "dvec_s.h"
#include <assert.h>
#include <string.h>
#include <stdio.h>
static const int freq[] = { 0, 1, 0, -1 };
void
parse_input(struct dvec *phases)
{
const char *c, *sep;
int *val;
sep = strchr(aoc.input, '\n');
assert(sep != NULL);
for (c = aoc.input; c < sep; c++) {
val = dvec_add_slot(phases);
*val = *c - '0';
}
}
void
fft(struct dvec *phases, size_t rounds)
{
struct dvec copy;
size_t r, i, k, l;
ssize_t sum;
int digit;
int *val;
dvec_init(©, sizeof(int), 0, &stdlib_strict_heap_allocator);
for (r = 0; r < rounds; r++) {
dvec_copy(©, phases);
for (i = 0; i < copy.len; i++) {
sum = 0;
for (k = 0; k < copy.len; k++) {
l = (k + 1) / (i + 1);
digit = *(int *)dvec_at(©, k);
sum += freq[l % 4] * digit;
}
sum = ABS(sum) % 10;
val = dvec_at(phases, i);
*val = (int) sum;
}
}
dvec_deinit(©);
}
void
fft_dup(struct dvec *phases, size_t offset, size_t rounds, size_t dup)
{
size_t r, i, len, lutlen;
int *lut, *lutc, *lutp;
int digit, *slot;
/* | a b c
* --+------------------------
* 1 | a+b+c b+c c
* 2 | a+2b+3c b+2c c
* n |a+nb+n(n+1)/2c b+nc c
*
* a+sum(1)b+sum(sum(1))c .. not nice
*
* sum(1): n
* sum(sum(1)): n(n+1)/2
* sum(sum(sum(1))): (K2+K1)/2 = (n^2+n)/2 + (n^3-n)/6
*
* .. calculation possible but not practically feasible since we
* would have to do 10000..th sum() .. will have to use a lookup table
*/
len = phases->len * dup;
assert(offset >= len / 2 && offset < len);
lutlen = len - offset;
lut = malloc(lutlen * sizeof(int) * (rounds + 1));
assert(lut != NULL);
/* top row */
for (i = 0; i < lutlen; i++) {
digit = *(int *)dvec_at(phases, (i + offset) % phases->len);
lut[i] = digit;
}
/* right column */
digit = *(int *)dvec_at(phases, (len - 1) % phases->len);
for (r = 0; r < rounds; r++) {
lut[(r + 1) * lutlen + lutlen - 1] = digit;
}
for (r = 0; r < rounds; r++) {
lutp = &lut[r * lutlen + lutlen - 2];
lutc = &lut[(r + 1) * lutlen + lutlen - 2];
for (i = 1; i < lutlen; i++, lutp--, lutc--)
lutc[0] = (lutp[0] + lutc[1]) % 10;
}
dvec_clear(phases);
for (i = 0; i < 8; i++) {
slot = dvec_add_slot(phases);
*slot = lut[rounds * lutlen + i];
}
free(lut);
}
void
part1(void)
{
struct dvec phases;
char *answer;
size_t i;
int digit;
dvec_init(&phases, sizeof(int), 64, &stdlib_strict_heap_allocator);
parse_input(&phases);
fft(&phases, 100);
answer = malloc(9);
for (i = 0; i < 8; i++) {
digit = *(int *)dvec_at(&phases, i);
answer[i] = '0' + (char) digit;
}
answer[i] = 0;
aoc.answer = answer;
aoc.solution = "29956495";
dvec_deinit(&phases);
}
void
part2(void)
{
struct dvec phases;
char *answer;
int digit;
size_t offset;
size_t base;
size_t i;
dvec_init(&phases, sizeof(int), 64, &stdlib_strict_heap_allocator);
parse_input(&phases);
base = 1;
offset = 0;
for (i = 0; i < 7; i++) {
digit = *(int *)dvec_at(&phases, 6 - i);
offset += base * (size_t) digit;
base *= 10;
}
fft_dup(&phases, offset, 100, 10000);
answer = malloc(9);
for (i = 0; i < 8; i++) {
digit = *(int *)dvec_at(&phases, i);
answer[i] = '0' + (char) digit;
}
answer[i] = 0;
aoc.answer = answer;
aoc.solution = "73556504";
dvec_deinit(&phases);
}
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