solve day 16
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day16.c
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282
day16.c
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#include <stdint.h>
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#include <stdio.h>
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#include <assert.h>
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#include <string.h>
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#include <sys/param.h>
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#include "types.h"
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#include "aoc.h"
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struct day16_valve {
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u32 id;
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char name[3];
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u32 flowrate;
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struct day16_valve **valves;
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u32 valve_count;
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};
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struct day16_data {
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struct day16_valve *valves;
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size_t count;
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};
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static struct day16_valve* find_valve_by_name(struct day16_valve* valves, size_t count, char *name)
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{
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for (size_t i = 0; i < count; i++) {
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if (valves[i].name[0] == name[0] && valves[i].name[1] == name[1]) {
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return &valves[i];
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}
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}
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return NULL;
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}
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static size_t count_char_in_str(char *str, char c)
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{
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size_t count = 0;
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for (size_t i = 0; i < strlen(str); i++) {
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count += (str[i] == c);
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}
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return count;
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}
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static void* day16_parse(char** lines, int line_count)
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{
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struct day16_data *data = malloc(sizeof(struct day16_data));
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data->count = line_count;
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data->valves = malloc(sizeof(struct day16_valve) * line_count);
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char *connections[line_count];
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for (size_t i = 0; i < line_count; i++) {
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struct day16_valve *valve = &data->valves[i];
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valve->id = i;
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valve->name[0] = lines[i][6];
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valve->name[1] = lines[i][7];
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valve->name[2] = 0;
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valve->flowrate = strtol(strchr(lines[i], '=')+1, NULL, 10);
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char *valves_word = strstr(lines[i], "valves");
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if (valves_word) {
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connections[i] = strstr(lines[i], "valves") + 7;
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} else {
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connections[i] = strstr(lines[i], "valve") + 6;
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}
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}
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for (int i = 0; i < line_count; i++) {
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struct day16_valve *valve = &data->valves[i];
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valve->valve_count = count_char_in_str(connections[i], ',') + 1;
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valve->valves = malloc(sizeof(struct day16_valve*) * valve->valve_count);
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int j = 0;
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for (char *tok = strtok(connections[i], ", "); tok; tok = strtok(NULL, ", ")) {
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valve->valves[j] = find_valve_by_name(data->valves, data->count, tok);
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j++;
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}
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}
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return data;
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}
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static void day16_get_nearby_closed_valves(
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struct day16_valve **valves, size_t valve_count,
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struct day16_valve **closed_valves, size_t *closed_count,
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size_t from_valve, u32 time_limit, size_t **distances,
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bool *opened
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)
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{
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*closed_count = 0;
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for (size_t i = 0; i < valve_count; i++) {
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struct day16_valve *valve = valves[i];
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if (opened[valve->id]) continue;
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u32 distance = distances[from_valve][valve->id];
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if (distance+1 < time_limit) {
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closed_valves[*closed_count] = valve;
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(*closed_count)++;
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}
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}
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}
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static void day16_get_nonzero_valves(
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struct day16_valve *valves, size_t valve_count,
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struct day16_valve **nonzero_valves, size_t *nonzero_count
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)
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{
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*nonzero_count = 0;
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for (size_t i = 0; i < valve_count; i++) {
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struct day16_valve *valve = &valves[i];
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if (valve->flowrate > 0) {
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nonzero_valves[*nonzero_count] = valve;
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(*nonzero_count)++;
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}
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}
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}
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static u32 day16_search(struct day16_valve **valves, size_t valve_count, size_t from_valve, u32 time_limit, size_t **distances, bool *opened)
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{
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struct day16_valve *closed_valves[valve_count];
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size_t closed_count = 0;
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day16_get_nearby_closed_valves(valves, valve_count, closed_valves, &closed_count, from_valve, time_limit, distances, opened);
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u32 best_preassure = 0;
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for (size_t i = 0; i < closed_count; i++) {
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struct day16_valve *valve = closed_valves[i];
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u32 distance = distances[from_valve][valve->id];
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opened[valve->id] = true;
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u32 preasure_from_subsequent = day16_search(valves, valve_count, valve->id, time_limit - distance - 1, distances, opened);
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opened[valve->id] = false;
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u32 preassure_released = (time_limit - distance - 1) * valve->flowrate;
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best_preassure = MAX(best_preassure, preasure_from_subsequent + preassure_released);
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}
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return best_preassure;
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}
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// Floyd-Warshall
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static size_t** day16_compute_distances(struct day16_valve *valves, size_t valve_count)
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{
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size_t **distances = malloc(sizeof(size_t*) * valve_count);
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for (size_t i = 0; i < valve_count; i++) {
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distances[i] = malloc(sizeof(size_t) * valve_count);
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}
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for (size_t i = 0; i < valve_count; i++) {
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struct day16_valve *valve = &valves[i];
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for (size_t j = 0; j < valve_count; j++) {
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distances[i][j] = valve_count;
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}
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distances[i][i] = 0;
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for (size_t j = 0; j < valve->valve_count; j++) {
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struct day16_valve *neighbour = valve->valves[j];
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distances[i][neighbour->id] = 1;
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distances[neighbour->id][i] = 1;
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}
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}
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for (size_t idx = 0; idx < valve_count; idx++) {
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for (size_t i = 0; i < valve_count; i++) {
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if (i == idx) continue;
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for (size_t j = 0; j < valve_count; j++) {
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if (j == idx) continue;
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if (i == j) continue;
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distances[i][j] = MIN(distances[i][j], distances[i][idx] + distances[idx][j]);
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}
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}
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}
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return distances;
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}
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static void day16_part1(void *p)
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{
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struct day16_data *data = (struct day16_data *)p;
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struct day16_valve *starting_valve = find_valve_by_name(data->valves, data->count, "AA");
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size_t** distances = day16_compute_distances(data->valves, data->count);
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bool opened[data->count];
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memset(opened, false, data->count * sizeof(bool));
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struct day16_valve *nonzero_valves[data->count];
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size_t nonzero_count = 0;
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day16_get_nonzero_valves(data->valves, data->count, nonzero_valves, &nonzero_count);
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u32 answer = day16_search(nonzero_valves, nonzero_count, starting_valve->id, 30, distances, opened);
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printf("%d\n", answer);
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}
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struct day16_part2_entry {
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u32 visited_bitmask;
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size_t current;
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u32 time_left;
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u32 preassure;
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};
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static bool day16_is_visited(u32 visited_bitmask, size_t id)
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{
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return (visited_bitmask & (1 << id)) > 0;
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}
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static void day16_part2(void *p)
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{
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struct day16_data *data = (struct day16_data *)p;
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struct day16_valve *starting_valve = find_valve_by_name(data->valves, data->count, "AA");
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size_t** distances = day16_compute_distances(data->valves, data->count);
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bool opened[data->count];
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memset(opened, false, data->count * sizeof(bool));
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struct day16_valve *nonzero_valves[data->count];
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size_t nonzero_count = 0;
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day16_get_nonzero_valves(data->valves, data->count, nonzero_valves, &nonzero_count);
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#define DAY16_MAX_STACK 256
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struct day16_part2_entry stack[DAY16_MAX_STACK] = { 0 };
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size_t stack_size = 0;
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assert(nonzero_count < 32);
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u32 traversal_combinations = 1 << nonzero_count;
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i32 best_preassures[traversal_combinations];
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for (size_t i = 0; i < traversal_combinations; i++) {
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best_preassures[i] = -1;
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}
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stack[0].time_left = 26;
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stack[0].current = starting_valve->id;
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stack_size = 1;
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while (stack_size > 0) {
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struct day16_part2_entry entry = stack[stack_size-1];
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stack_size--;
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best_preassures[entry.visited_bitmask] = MAX(best_preassures[entry.visited_bitmask], (i32)entry.preassure);
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for (size_t i = 0; i < nonzero_count; i++) {
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struct day16_valve *valve = nonzero_valves[i];
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if (day16_is_visited(entry.visited_bitmask, i)) continue;
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u32 distance = distances[entry.current][valve->id];
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if (entry.time_left <= distance+1) continue;
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assert(stack_size+1 < DAY16_MAX_STACK);
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struct day16_part2_entry *new_entry = &stack[stack_size];
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i32 time_left = entry.time_left - distance - 1;
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new_entry->current = valve->id;
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new_entry->time_left = time_left;
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new_entry->preassure = entry.preassure + time_left * valve->flowrate;
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new_entry->visited_bitmask = entry.visited_bitmask | (1 << i);
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stack_size++;
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}
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}
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i32 best_preassure_overall = -1;
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for (size_t i = 1; i < traversal_combinations; i++) {
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if (best_preassures[i] == -1) continue;
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for (size_t j = 1; j < traversal_combinations; j++) {
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if ((i & j) > 0) continue;
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if (best_preassures[j] == -1) continue;
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best_preassure_overall = MAX(best_preassures[i] + best_preassures[j], best_preassure_overall);
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}
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}
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printf("%d\n", best_preassure_overall);
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}
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ADD_SOLUTION(16, day16_parse, day16_part1, day16_part2);
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