Add the implementation of Skiplist

Author: souravpalitrana

LinkedList/DesignSkipList/src/designskiplist/DesignSkipList.java

@@ -0,0 +1,27 @@
+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package designskiplist;
+
+/**
+ *
+ * @author souravpalit
+ */
+public class Node {
+    
+    public int val;
+    public Node next;
+    public Node down;
+    
+    public Node(int val) {
+        this.val = val;
+    }
+    
+    public Node(int val, Node next, Node down) {
+        this.val = val;
+        this.down = down;
+        this.next = next;
+    }
+}

LinkedList/DesignSkipList/src/designskiplist/Node.java

@@ -0,0 +1,96 @@
+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package designskiplist;
+
+import java.util.Random;
+import java.util.Stack;
+
+/**
+ *
+ * @author souravpalit
+ */
+public class SkipList {
+
+    private Node head;
+    private int DUMMY_VALUE = -1;
+    private Random randomGenerator;
+
+    public SkipList() {
+        head = new Node(DUMMY_VALUE); // dummy Node
+        randomGenerator = new Random();
+    }
+
+    public boolean search(int target) {
+        Node current = head;
+
+        while (current != null) {
+            while (current.next != null && current.next.val < target) {
+                current = current.next;
+            }
+
+            if (current.next != null && current.next.val == target) {
+                return true;
+            }
+            // Not found so go down
+            current = current.down;
+        }
+
+        return false;
+    }
+
+    public void add(int target) {
+        Stack<Node> path = new Stack<Node>();
+        Node current = head;
+        while (current != null) {
+            while (current.next != null && current.next.val < target) {
+                current = current.next;
+            }
+
+            path.push(current);
+            current = current.down;
+        }
+
+        boolean goUp = true;
+        Node down = null;
+
+        while (goUp && !path.isEmpty()) {
+            current = path.pop();
+            current.next = new Node(target, current.next, down);
+            down = current.next;
+            goUp = getRandomNumber(1, 100) < 50;
+        }
+        
+        if (goUp) {
+            head = new Node(DUMMY_VALUE, null, head);;
+        }
+
+    }
+
+    public boolean erase(int target) {
+        Node current = head;
+        boolean found = false;
+
+        while (current != null) {
+            while (current.next != null && current.next.val < target) {
+                current = current.next;
+            }
+
+            if (current.next != null && current.next.val == target) {
+                found = true;
+                current.next = current.next.next;
+            }
+
+            // May present down also
+            current = current.down;
+        }
+
+        return found;
+    }
+
+    public int getRandomNumber(int min, int max) {
+        return randomGenerator.nextInt(max - min) + min;
+    }
+}