Added treap class

src/main/java/com/thealgorithms/datastructures/trees/Treap.java

@@ -0,0 +1,357 @@
+package com.thealgorithms.datastructures.trees;
+
+import java.util.Random;
+
+/**
+ * Treap -> Tree + Heap
+ * Also called as cartesian tree
+ *
+ * @see
+ * <a href = "https://cp-algorithms.com/data_structures/treap.html" />
+ */
+
+public class Treap {
+
+    public static class TreapNode {
+        /**
+         * TreapNode class defines the individual nodes in the Treap
+         *
+         * value -> holds the value of the node.
+         * Binary Search Tree is built based on value.
+         *
+         * priority -> holds the priority of the node.
+         * Heaps are maintained based on priority.
+         * It is randomly assigned
+         *
+         * size -> holds the size of the subtree with current node as root
+         *
+         * left -> holds the left subtree
+         * right -> holds the right subtree
+         */
+        public int value;
+        private int priority;
+        private int size;
+        public TreapNode left;
+        public TreapNode right;
+
+        public TreapNode(int valueParam, int priorityParam) {
+            value = valueParam;
+            priority = priorityParam;
+            size = 1;
+            left = null;
+            right = null;
+        }
+
+        /**
+         * updateSize -> updates the subtree size of the current node
+         */
+        private void updateSize() {
+            size = 1;
+            if (left != null) {
+                size += left.size;
+            }
+            if (right != null) {
+                size += right.size;
+            }
+        }
+    }
+
+    /**
+     * root -> holds the root node in the Treap
+     * random -> to generate random priority for the nodes in the Treap
+     */
+    private TreapNode root;
+    private Random random = new Random();
+
+    /**
+     * Constructors
+     *
+     * Treap() -> create an empty Treap
+     * Treap(int[] nodeValues) -> add the elements given in the array to the Treap
+     */
+    public Treap() {
+        root = null;
+    }
+
+    /**
+     * merges two Treaps left and right into a single Treap
+     *
+     * @param left left Treap
+     * @param right right Treap
+     * @return root of merged Treap
+     */
+    private TreapNode merge(TreapNode left, TreapNode right) {
+        if (left == null) {
+            return right;
+        }
+        if (right == null) {
+            return left;
+        }
+
+        if (left.priority > right.priority) {
+            left.right = merge(left.right, right);
+            left.updateSize();
+            return left;
+        } else {
+            right.left = merge(left, right.left);
+            right.updateSize();
+            return right;
+        }
+    }
+
+    /**
+     * split the Treap into two Treaps where left Treap has nodes <= key and right Treap has nodes > key
+     *
+     * @param node root node to be split
+     * @param key key to compare the nodes
+     * @return TreapNode array of size 2.
+     * TreapNode[0] contains the root of left Treap after split
+     * TreapNode[1] contains the root of right Treap after split
+     */
+    private TreapNode[] split(TreapNode node, int key) {
+        if (node == null) {
+            return new TreapNode[] {null, null};
+        }
+
+        TreapNode[] result;
+
+        if (node.value <= key) {
+            result = split(node.right, key);
+            node.right = result[0];
+            node.updateSize();
+            result[0] = node;
+        } else {
+            result = split(node.left, key);
+            node.left = result[1];
+            node.updateSize();
+            result[1] = node;
+        }
+
+        return result;
+    }
+
+    /**
+     * insert a node into the Treap
+     *
+     * @param value value to be inserted into the Treap
+     * @return root of the Treap where the value is inserted
+     */
+    public TreapNode insert(int value) {
+        if (root == null) {
+            root = new TreapNode(value, random.nextInt());
+            return root;
+        }
+
+        TreapNode[] splitted = split(root, value);
+
+        TreapNode node = new TreapNode(value, random.nextInt());
+
+        TreapNode tempMerged = merge(splitted[0], node);
+        tempMerged.updateSize();
+
+        TreapNode merged = merge(tempMerged, splitted[1]);
+        merged.updateSize();
+
+        root = merged;
+
+        return root;
+    }
+
+    /**
+     * delete a value from root if present
+     *
+     * @param value value to be deleted from the Treap
+     * @return root of the Treap where delete has been performed
+     */
+    public TreapNode delete(int value) {
+        root = deleteNode(root, value);
+        return root;
+    }
+
+    private TreapNode deleteNode(TreapNode root, int value) {
+        if (root == null) {
+            return null;
+        }
+
+        if (value < root.value) {
+            root.left = deleteNode(root.left, value);
+        } else if (value > root.value) {
+            root.right = deleteNode(root.right, value);
+        } else {
+            root = merge(root.left, root.right);
+        }
+
+        if (root != null) {
+            root.updateSize();
+        }
+        return root;
+    }
+
+    /**
+     * print inorder traversal of the Treap
+     */
+    public void inOrder() {
+        System.out.print("{");
+        printInorder(root);
+        System.out.print("}");
+    }
+
+    private void printInorder(TreapNode root) {
+        if (root == null) {
+            return;
+        }
+        printInorder(root.left);
+        System.out.print(root.value + ",");
+        printInorder(root.right);
+    }
+
+    /**
+     * print preOrder traversal of the Treap
+     */
+    public void preOrder() {
+        System.out.print("{");
+        printPreOrder(root);
+        System.out.print("}");
+    }
+
+    private void printPreOrder(TreapNode root) {
+        if (root == null) {
+            return;
+        }
+        System.out.print(root.value + ",");
+        printPreOrder(root.left);
+        printPreOrder(root.right);
+    }
+
+    /**
+     * print postOrder traversal of the Treap
+     */
+    public void postOrder() {
+        System.out.print("{");
+        printPostOrder(root);
+        System.out.print("}");
+    }
+
+    private void printPostOrder(TreapNode root) {
+        if (root == null) {
+            return;
+        }
+        printPostOrder(root.left);
+        printPostOrder(root.right);
+        System.out.print(root.value + ",");
+    }
+
+    /**
+     * Search a value in the Treap
+     *
+     * @param value value to be searched for
+     * @return node containing the value
+     * null if not found
+     */
+    public TreapNode search(int value) {
+        return searchVal(root, value);
+    }
+
+    private TreapNode searchVal(TreapNode root, int value) {
+        if (root == null) {
+            return null;
+        }
+
+        if (root.value == value) {
+            return root;
+        } else if (root.value < value) {
+            return searchVal(root.right, value);
+        } else {
+            return searchVal(root.left, value);
+        }
+    }
+
+    /**
+     * find the lowerBound of a value in the Treap
+     *
+     * @param value value for which lowerBound is to be found
+     * @return node which is the lowerBound of the value passed
+     */
+    public TreapNode lowerBound(int value) {
+        TreapNode lowerBoundNode = null;
+        TreapNode current = root;
+
+        while (current != null) {
+            if (current.value >= value) {
+                lowerBoundNode = current;
+                current = current.left;
+            } else {
+                current = current.right;
+            }
+        }
+
+        return lowerBoundNode;
+    }
+
+    /**
+     * find the upperBound of a value in the Treap
+     *
+     * @param value value for which upperBound is to be found
+     * @return node which is the upperBound of the value passed
+     */
+    public TreapNode upperBound(int value) {
+        TreapNode upperBoundNode = null;
+        TreapNode current = root;
+
+        while (current != null) {
+            if (current.value > value) {
+                upperBoundNode = current;
+                current = current.left;
+            } else {
+                current = current.right;
+            }
+        }
+
+        return upperBoundNode;
+    }
+
+    /**
+     * returns size of the Treap
+     */
+    public int size() {
+        if (root == null) {
+            return 0;
+        }
+        return root.size;
+    }
+
+    /**
+     * returns if Treap is empty
+     */
+    public boolean isEmpty() {
+        return root == null;
+    }
+
+    /**
+     * returns root node of the Treap
+     */
+    public TreapNode getRoot() {
+        return root;
+    }
+
+    /**
+     * returns left node of the TreapNode
+     */
+    public TreapNode getLeft(TreapNode node) {
+        return node.left;
+    }
+
+    /**
+     * returns the right node of the TreapNode
+     */
+    public TreapNode getRight(TreapNode node) {
+        return node.right;
+    }
+
+    /**
+     * prints the value, priority, size of the subtree of the TreapNode, left TreapNode and right TreapNode of the node
+     */
+    public String toString(TreapNode node) {
+        return "{value : " + node.value + ", priority : " + node.priority + ", subTreeSize = " + node.size + ", left = " + node.left + ", right = " + node.right + "}";
+    }
+}