SkipList written by java

Author: huzheng

template/sort/SkipList.java

@@ -0,0 +1,200 @@
+import org.junit.Assert;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+public class SkipList {
+
+  private static class Node {
+    int value;
+    Node left, down;
+
+    Node(int x) {
+      this(x, null, null);
+    }
+
+    Node(int x, Node down, Node left) {
+      this.value = x;
+      this.down = down;
+      this.left = left;
+    }
+  }
+
+  private List<Node> head;
+  private double p;
+  private int size;
+  private Random rand;
+
+  public SkipList(double p, int maxHeight) {
+    this.head = new ArrayList<Node>();
+    this.p = p;
+    this.size = 0;
+    assert maxHeight > 0;
+    for (int i = 0; i < maxHeight; i++) {
+      head.add(new Node(0));
+      if (i > 0) {
+        head.get(i).down = head.get(i - 1);
+      }
+    }
+    rand = new Random();
+  }
+
+  public SkipList() {
+    this(0.5, 32);
+  }
+
+  private int randomHeight() {
+    int h = 0;
+    while (rand.nextDouble() < p && h < 64)
+      h++;
+    return h + 1;
+  }
+
+  public void add(int value) {
+    final int maxHeight = head.size();
+    Node[] update = new Node[maxHeight];
+    Node it = head.get(maxHeight - 1);
+    int h = maxHeight - 1;
+    while (it != null) {
+      if (it.left == null || value < it.left.value) {
+        update[h--] = it;
+        it = it.down;
+      } else {
+        it = it.left;
+      }
+    }
+    int currentHeight = randomHeight();
+    Node[] current = new Node[currentHeight];
+    for (h = 0; h < currentHeight; h++) {
+      current[h] = new Node(value);
+      if (h > 0) {
+        current[h].down = current[h - 1];
+      }
+    }
+    if (maxHeight < currentHeight) {
+      for (h = maxHeight; h < currentHeight; h++) {
+        head.add(new Node(0, head.get(h - 1), current[h]));
+      }
+      for (h = 0; h < maxHeight; h++) {
+        current[h].left = update[h].left;
+        update[h].left = current[h];
+      }
+    } else {
+      for (h = 0; h < currentHeight; h++) {
+        current[h].left = update[h].left;
+        update[h].left = current[h];
+      }
+    }
+    size++;
+  }
+
+  public boolean found(int value) {
+    final int maxHeight = head.size();
+    Node it = head.get(maxHeight - 1);
+    while (it != null) {
+      if (it.left == null || value <= it.left.value) {
+        if (it.left != null && it.left.value == value) return true;
+        it = it.down;
+      } else {
+        it = it.left;
+      }
+    }
+    return false;
+  }
+
+  public boolean remove(int value) {
+    final int maxHeight = head.size();
+    Node it = head.get(maxHeight - 1);
+    boolean isFound = false;
+    while (it != null) {
+      if (it.left == null || value <= it.left.value) {
+        if (it.left != null && it.left.value == value) {
+          // do the removing
+          isFound = true;
+          it.left = it.left.left;
+        }
+        it = it.down;
+      } else {
+        it = it.left;
+      }
+    }
+    if (isFound) {
+      for (int i = head.size() - 1; i >= 1; i--) {
+        if (head.get(i).left == null) {
+          head.remove(i);
+        }
+      }
+      --size;
+    }
+    return isFound;
+  }
+
+  public int[] toArrays() {
+    int i = 0;
+    int[] values = new int[size];
+    for (Node it = head.get(0).left; it != null; it = it.left) {
+      values[i++] = it.value;
+    }
+    return values;
+  }
+
+  public int size() {
+    return size;
+  }
+
+  public void print() {
+    for (int i = head.size() - 1; i >= 0; i--) {
+      Node it = head.get(i).left;
+      System.out.print("Height #" + i + ": ");
+      while (it != null) {
+        System.out.print(it.value + " ");
+        it = it.left;
+      }
+      System.out.println();
+
+    }
+  }
+
+  public static void main(String args[]) {
+    SkipList skipList = new SkipList();
+    int[] values1 = new int[] { 23, 12, 33, 45, 8, 1, 48, 49, 32, 24, 0, 88 };
+    int[] result1 = new int[] { 0, 1, 8, 12, 23, 24, 32, 33, 45, 48, 49, 88 };
+    for (int i = 0; i < values1.length; i++) {
+      skipList.add(values1[i]);
+    }
+    skipList.print();
+
+    Assert.assertEquals(skipList.size(), result1.length);
+    Assert.assertArrayEquals(result1, skipList.toArrays());
+
+    Assert.assertTrue(skipList.remove(0));
+    Assert.assertEquals(skipList.size(), result1.length - 1);
+    Assert.assertArrayEquals(new int[] { 1, 8, 12, 23, 24, 32, 33, 45, 48, 49, 88 },
+      skipList.toArrays());
+
+    Assert.assertFalse(skipList.remove(0));
+    Assert.assertEquals(skipList.size(), result1.length - 1);
+    Assert.assertArrayEquals(new int[] { 1, 8, 12, 23, 24, 32, 33, 45, 48, 49, 88 },
+      skipList.toArrays());
+
+    Assert.assertTrue(skipList.remove(88));
+    Assert.assertEquals(skipList.size(), result1.length - 2);
+    Assert.assertArrayEquals(new int[] { 1, 8, 12, 23, 24, 32, 33, 45, 48, 49 },
+      skipList.toArrays());
+
+    Assert.assertTrue(skipList.remove(33));
+    Assert.assertEquals(skipList.size(), result1.length - 3);
+    Assert.assertArrayEquals(new int[] { 1, 8, 12, 23, 24, 32, 45, 48, 49 }, skipList.toArrays());
+
+    Assert.assertTrue(skipList.remove(12));
+    Assert.assertEquals(skipList.size(), result1.length - 4);
+    Assert.assertArrayEquals(new int[] { 1, 8, 23, 24, 32, 45, 48, 49 }, skipList.toArrays());
+
+    for (int value : skipList.toArrays()) {
+      Assert.assertTrue(skipList.remove(value));
+    }
+    Assert.assertTrue(skipList.size() == 0);
+  }
+}
+