/*
 * MEDIUM: Sequential Linked List Traversal
 * =========================================
 * This program creates a linked list with nodes allocated contiguously,
 * representing the best-case scenario for linked lists.
 * Still slower than arrays due to pointer chasing overhead.
 *
 * Compile: make list_sequential
 * Run:     ./list_sequential
 * Profile: perf stat -e cache-misses,cache-references ./list_sequential
 */

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define N 10000000  /* 10 million elements */

struct node {
    int value;
    struct node *next;
};

double get_time(void) {
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return ts.tv_sec + ts.tv_nsec / 1e9;
}

long sum_list(struct node *head) {
    long sum = 0;
    struct node *curr = head;
    while (curr != NULL) {
        sum += curr->value;
        curr = curr->next;
    }
    return sum;
}

/*
 * Create linked list with nodes allocated sequentially (best case for list)
 * All nodes allocated in one contiguous block, linked in order.
 */
struct node *create_list_sequential(int n) {
    struct node *nodes = malloc(n * sizeof(struct node));
    if (!nodes) {
        perror("malloc list");
        exit(1);
    }

    for (int i = 0; i < n - 1; i++) {
        nodes[i].value = i % 100;
        nodes[i].next = &nodes[i + 1];
    }
    nodes[n - 1].value = (n - 1) % 100;
    nodes[n - 1].next = NULL;

    return nodes;
}

int main(void) {
    printf("Sequential Linked List Traversal (%d elements)\n", N);
    printf("All nodes allocated contiguously - best case for linked list.\n");
    printf("Still has pointer chasing overhead vs array.\n\n");

    printf("Creating sequential linked list...\n");
    struct node *list = create_list_sequential(N);

    /* Warm up */
    sum_list(list);

    double start = get_time();
    long result = sum_list(list);
    double elapsed = get_time() - start;

    printf("Sequential list sum: %ld in %.4f seconds\n\n", result, elapsed);

    printf("To see cache behavior, run:\n");
    printf("  perf stat -e cache-misses,cache-references ./list_sequential\n");

    free(list);
    return 0;
}