LInkedListDemo 1

class linkedlistdemo1 {
  static int[] data = new int[12];
  static int[] next = new int[12];
  static int HEAD, FREE;

  public static void initList() {
    int i;
    // -1 is used to indicate NULL pointer values
    HEAD = -1; // Empty List
    FREE = 0; // The free list starts with first node
    for (i=0; i<12; i++) {
      // initializes to nodes to 0
      // in fact any values can be used
      data[i] = 0;
      // initialize the free list
      // to include all nodes
      // FREE -> 0 -> 1 -> 2 -> 3 ..... 10 -> 11 -> -1
      next[i] = i+1;
      // The last node in the array
      if (i == 11) {
        next[i] = -1;
      }
    }
  }

  public static int getFreeNode() {
    int nodeID;
    // If there are available elements
    if (FREE != -1) {
      nodeID = FREE;
      FREE = next[FREE];
    } else {
      // Return -1
      // No more free nodes
      nodeID = -1;
    }
    return nodeID;
  }

  public static void returnFreeNode(int nodeID) {
      next[nodeID] = FREE;
      FREE = nodeID;
  }

  public static void removeBegin() {
    int temp;
    if (HEAD != -1) {
      temp = HEAD;
      HEAD = next[HEAD];
      returnFreeNode(temp);
    }
  }

  public static boolean insertAfter(int item, int pos){
    int temp;
    int count, prev, current;
    temp = getFreeNode();
    if (temp != -1) {
      if (pos == 0) {
        data[temp] = item;
        next[temp] = HEAD;
        HEAD = temp;
        return true;
      } else {
        count = 0;
        prev = HEAD;
        current = HEAD;
        while (current != -1 && count < pos) {
          prev = current;
          current = next[current];
          count++;
        }
        data[temp] = item;
        next[temp] = current;
        next[prev] = temp;
        return true;
      }
    } else
      return false;
  }

  public static boolean insertBegin(int item){
    return insertAfter(item, 0);
  }

  public static int countList() {
    int result=0;
    int current;
    current = HEAD;
    while (current != -1) {
      result++;
      current = next[current];
    }
    return result;
  }

  public static void printList() {
    int i;
    i = HEAD;
    System.out.print("HEAD -> ");
    while (i != -1) {
      System.out.printf("%d -> ", data[i]);
      i = next[i];
    }
    System.out.println("END");
  }

  public static void printFreeList() {
    int i;
    i = FREE;
    System.out.print("FREE -> ");
    while (i != -1) {
      System.out.printf("[%d] -> ", i);
      i = next[i];
    }
    System.out.println("END");
  }

  public static void main(String[] args) {
    initList();
    insertBegin(9);
    insertBegin(8);
    insertBegin(7);
    printList();
    System.out.printf("Number of elements: %d\n",countList());

  }


}