adventofcode2024/day22/c/day22.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <omp.h>

#define CHARS_MAX 64
#define MAX_BUYERS 8*1024
#define GENERATION 2000

typedef struct node {
    struct node *children[19];
    uint64_t value;
    char key;
    uint8_t is_leaf;
} node_t;

node_t* create_node() {
    node_t *node = calloc(1, sizeof(node[0]));
    return node;
}

node_t* search(node_t* root, int8_t* word, int len) {
    node_t* node = root;
    for (int i = 0; i < len; i++) {
        if (node->children[word[i] + 9] == NULL) {
            return NULL;
        }
        node = node->children[word[i] + 9];
    }
    return node;
}

void insert(node_t* root, int8_t* word, int len, uint64_t value) {
    node_t* node = root;
    for (int i = 0; i < len; i++) {
        if (node->children[word[i] + 9] == NULL) {
            node->children[word[i] + 9] = create_node();
        }
        node = node->children[word[i] + 9];
    }
    node->value = value;
    node->is_leaf = 1;
}

void free_node(node_t* node) {
    for (int i = 0; i < 19; i++) {
        if (node->children[i] != NULL) {
            free_node(node->children[i]);
        }
    }

    free(node);
}

uint64_t generate_new_secret(uint64_t);
uint64_t mix(uint64_t, uint64_t);
uint64_t prune(uint64_t);

int main() {
    char *p, *buf, c;

    buf = calloc(CHARS_MAX, sizeof(char));
    p = buf;

    uint64_t *secrets = calloc(MAX_BUYERS, sizeof(secrets[0]));
    int secret_count = 0;

    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c != '\n') {
            continue;
        }

        sscanf(buf, "%lu", &secrets[secret_count++]);

        memset(buf, 0, CHARS_MAX);
        p = buf;
    }
    free(buf);

    uint64_t sum = 0;
    uint64_t **prices = calloc(secret_count, sizeof(prices[0]));
    for (int i = 0; i < secret_count; i++) {
        prices[i] = calloc(GENERATION + 1, sizeof(prices[0][0]));
        prices[i][0] = secrets[i] % 10;
        for (int j = 0; j < GENERATION; j++) {
            secrets[i] = generate_new_secret(secrets[i]);
            prices[i][j+1] = secrets[i] % 10;
        }
        sum += secrets[i];
    }
    printf("%lu\n", sum);

    free(secrets);

    // Calculate diffs
    int8_t **diffs = calloc(secret_count, sizeof(diffs[0]));
    for (int i = 0; i < secret_count; i++) {
        diffs[i] = calloc(GENERATION, sizeof(diffs[0][0]));
        for (int j = 0; j < GENERATION; j++) {
            diffs[i][j] = (int8_t)prices[i][j+1] - (int8_t)prices[i][j];
        }
    }

    int8_t (**sequences)[4] = calloc(secret_count, sizeof(int8_t(*)[4]));
    for (int i = 0; i < secret_count; i++) {
        sequences[i] = calloc(GENERATION - 4, sizeof(int8_t[4]));
        for (int j = 0; j < GENERATION-4; j++) {
            sequences[i][j][0] = diffs[i][j];
            sequences[i][j][1] = diffs[i][j+1];
            sequences[i][j][2] = diffs[i][j+2];
            sequences[i][j][3] = diffs[i][j+3];
        }
        free(diffs[i]);
    }
    free(diffs);

    node_t *root = calloc(1, sizeof(node_t));

    uint64_t max_bananas = 0;
    for (int i = 0; i < secret_count; i++) {
        for (int j = 0; j < GENERATION - 4; j++) {
            int8_t pattern[4];
            memcpy(pattern, sequences[i][j], sizeof(sequences[0][0]));

            node_t *node  = search(root, pattern, 4);

            if (node != NULL && node->is_leaf) {
                continue;
            }

            // Count bananas
            uint64_t bananas = 0;
#pragma omp parallel for
            for (int k = 0; k < secret_count; k++) {
                for (int l = 0; l < GENERATION - 4; l++) {
                    if (memcmp(pattern, sequences[k][l], sizeof(sequences[0][0]))) {
                        continue;
                    }
                    
#pragma omp critical
                    {
                        bananas += prices[k][l+4];
                    }
                    break;
                }
            }

            insert(root, pattern, 4, bananas);

            if (bananas > max_bananas) {
                max_bananas = bananas;
            }
        }
    }

    printf("%lu\n", max_bananas);


    for (int i = 0; i < secret_count; i++) {
        free(prices[i]);
        free(sequences[i]);
    }

    free_node(root);
    free(prices);
    free(sequences);
}

uint64_t generate_new_secret(uint64_t secret) {
    uint64_t new_secret = secret;
    // 1
    new_secret = prune(mix(new_secret, new_secret * 64));
    // 2
    new_secret = prune(mix(new_secret, new_secret / 32));
    // 3
    new_secret = prune(mix(new_secret, new_secret * 2048));

    return new_secret;
}

uint64_t mix(uint64_t secret, uint64_t value) {
    return secret ^ value;
}

uint64_t prune(uint64_t secret) {
    return secret % 16777216;
}