#include <stdio.h>

typedef struct st st;
typedef struct node node; // forward declaration

typedef struct node {
    const void* key;
    void* value;
    node* prev;
    node* next;
} node;

struct st {
    node* head;
    node* tail;
};

// add new node to the end
void st_add(st table, void* key, void* value) {
    node n = {key, value, table.tail};
    if (table.head == NULL) {
        table.head = &n;
        table.tail = &n;
    }
    else {
        (*(table.tail)).next = &n;
        table.tail = &n;
    }  
}

void* nodeSearch(node* n, void* key) {
    if (n != NULL) {
        if ((*n).key == key) {
            return (*n).value;
        }
        else {
            return nodeSearch((*n).next, key);
        }
    }
    else {
        return NULL;
    }
}

// returns the pointer to key of the specified node, or null, if it does not exist
void* st_search(st table, void* key) {
    return nodeSearch(table.head, key);
}