/* SI 486D Spring 2013
   This is a skeleton for a skip list class that only supports
   insertion of height-1 nodes.

   Nodes are stored in "towers" which contain a list of forward-facing
   links ("flinks"), as well as a key and a value.

   To demo on a small random example, run 'javac SkipList.java && java SkipList"
*/

import java.util.*;

public class SkipList<V> {
  class Tower {
    double key;
    V value;
    ArrayList<Tower> flinks;

    Tower(int h, double key, V value) {
      this.key = key;
      this.value = value;
      this.flinks = new ArrayList<Tower>(Collections.nCopies(h+1, (Tower)null));
    }
  }

  Tower start;
  Tower end;
  int thesize = 0;

  public SkipList() {
    this.start = new Tower(0, Double.NEGATIVE_INFINITY, null);
    this.end = new Tower(0, Double.POSITIVE_INFINITY, null);
    this.start.flinks.set(0, this.end);
  }

  public int height() {
    return this.start.flinks.size()- 1;
  }

  public int size() {
    return this.thesize;
  }

  public void insert(double key, V value) {
    int h = 1; // TODO: choose height randomly!
    Tower newTower = new Tower(h, key, value);

    // Grow height of start/end as needed
    while (h >= this.height()) {
      this.start.flinks.add(this.end);
      this.end.flinks.add(null);
    }

    Tower currentTower = this.start;
    int level = currentTower.flinks.size()-1;
    while (level >= 0) {
      if (key > currentTower.flinks.get(level).key) {
        // Move right if we can on this level
        currentTower = currentTower.flinks.get(level);
      } 
      else {
        // Otherwise go down a level
        if (level <= h) {
          // Insert the new tower on this level
          newTower.flinks.set(level, currentTower.flinks.get(level));
          currentTower.flinks.set(level, newTower);
        }
        level -= 1;
      }
    }

    this.thesize += 1;
  }

  public String toString() {
    /* Returns a nice pretty representation of the skip list */
    String toret = "";
    for (int level = this.height(); level >= 0; --level) {
      Tower currentTower = this.start;
      while (currentTower != this.end) {
        String rep = "(" + Double.toString(currentTower.key) + ")";
        if (level >= currentTower.flinks.size()) {
          for (int i=0; i < rep.length(); ++i) toret += "-";
        }
        else { toret = toret + rep; }
        toret = toret + "--";
        currentTower = currentTower.flinks.get(0);
      }
      toret = toret + "(" + Double.toString(currentTower.key) + ")\n";
    }
    return toret;
  }

  public static void main(String[] args) {
    Random r = new Random();
    // Randomly insert 10 numbers and print the resulting skip list
    SkipList<String> S = new SkipList<String>();
    for (int i=0; i<7; ++i) {
      S.insert(r.nextInt(100), "this is the value");
    }
    System.out.println(S);
  }
}