From 4742ac4d53a88d5d21e2fca5ac3d5f5ae68dc0a0 Mon Sep 17 00:00:00 2001
From: wangzheng <wangzheng>
Date: Sun, 28 Oct 2018 23:01:45 +0800
Subject: [PATCH] 17 skiplist

---
 java/17_skiplist/SkipList.java | 119 +++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 java/17_skiplist/SkipList.java

diff --git a/java/17_skiplist/SkipList.java b/java/17_skiplist/SkipList.java
new file mode 100644
index 0000000..f6bcd70
--- /dev/null
+++ b/java/17_skiplist/SkipList.java
@@ -0,0 +1,119 @@
+package skiplist;
+
+import java.util.Random;
+
+/**
+ * 跳表的一种实现方法。
+ * 跳表中存储的是正整数，并且存储的是不重复的。
+ *
+ * Author：ZHENG
+ */
+public class SkipList {
+
+  private static final int MAX_LEVEL = 16;
+
+  private int levelCount = 1;
+
+  private Node head = new Node();  // 带头链表
+
+  private Random r = new Random();
+
+  public Node find(int value) {
+    Node p = head;
+    for (int i = levelCount - 1; i >= 0; --i) {
+      while (p.forwords[i] != null && p.forwords[i].data < value) {
+        p = p.forwords[i];
+      }
+    }
+
+    if (p.forwords[0] != null && p.forwords[0].data == value) {
+      return p.forwords[0];
+    } else {
+      return null;
+    }
+  }
+
+  public void insert(int value) {
+    int level = randomLevel();
+    Node newNode = new Node();
+    newNode.data = value;
+    newNode.maxLevel = level;
+    Node update[] = new Node[level];
+    for (int i = 0; i < level; ++i) {
+      update[i] = head;
+    }
+
+    Node p = head;
+    for (int i = level - 1; i >= 0; --i) {
+      while (p.forwords[i] != null && p.forwords[i].data < value) {
+        p = p.forwords[i];
+      }
+      update[i] = p;
+    }
+
+    for (int i = 0; i < level; ++i) {
+      newNode.forwords[i] = update[i].forwords[i];
+      update[i].forwords[i] = newNode;
+    }
+
+    if (levelCount < level) levelCount = level;
+  }
+
+  public void delete(int value) {
+    Node[] update = new Node[levelCount];
+    Node p = head;
+    for (int i = levelCount - 1; i >= 0; --i) {
+      while (p.forwords[i] != null && p.forwords[i].data < value) {
+        p = p.forwords[i];
+      }
+      update[i] = p;
+    }
+
+    if (p.forwords[0] != null && p.forwords[0].data == value) {
+      for (int i = levelCount - 1; i >= 0; --i) {
+        if (update[i].forwords[i] != null && update[i].forwords[i].data == value) {
+          update[i].forwords[i] = update[i].forwords[i].forwords[i];
+        }
+      }
+    }
+  }
+
+  private int randomLevel() {
+    int level = 1;
+    for (int i = 1; i < MAX_LEVEL; ++i) {
+      if (r.nextInt() % 2 == 1) {
+        level++;
+      }
+    }
+
+    return level;
+  }
+
+  public void printAll() {
+    Node p = head;
+    while (p.forwords[0] != null) {
+      System.out.print(p.forwords[0] + " ");
+      p = p.forwords[0];
+    }
+    System.out.println();
+  }
+
+  public class Node {
+    private int data = -1;
+    private Node forwords[] = new Node[MAX_LEVEL];
+    private int maxLevel = 0;
+
+    @Override
+    public String toString() {
+      StringBuilder builder = new StringBuilder();
+      builder.append("{ data: ");
+      builder.append(data);
+      builder.append("; levels: ");
+      builder.append(maxLevel);
+      builder.append(" }");
+
+      return builder.toString();
+    }
+  }
+
+}