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RedBlackTree.java
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RedBlackTree.java
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package ds.balanced_tree;
/*
Red-Black Tree is a self-balancing Binary Search Tree (BST) where every node follows following rules.
1) Every node has a color either red or black.
2) Root of tree is always black.
3) There are no two adjacent red nodes (A red node cannot have a red parent or red child).
4) Every path from root to a NULL node has same number of black nodes.
*/
public class RedBlackTree<E extends Comparable<E>> {
private RBNode<E> root;
public void insert(E elem) {
if (elem == null) throw new IllegalArgumentException();
if (root == null) root = new RBNode<>(elem, null, Color.BLACK); // if it is root node
else root = insertHelper(root, root, elem); // if it is not root node
}
private RBNode<E> insertHelper(RBNode<E> node, RBNode<E> parent, E elem) {
// usual insert
if (node == null) return new RBNode<>(elem, parent, Color.RED);
if (node.elem.compareTo(elem) > 0) node.left = insertHelper(node.left, node, elem);
else if (node.elem.compareTo(elem) < 0) node.right = insertHelper(node.right, node, elem);
if (node.color == Color.BLACK) return node; // the parent of current node is black
else { // the parent of current node is red
if (node.parent.left != null && node.parent.left.color == Color.RED &&
node.parent.right != null && node.parent.right.color == Color.RED) { // uncle node is red
if (node.parent.parent == null) node = recoloring(node, true); // parent is root node
else {
node = recoloring(node, false); //parent is not root node
}
} else { // uncle node is black, not red, then we have to rotate it
// like a AVL tree we have 4 rotating case
// case 1: right-right
if (node.right != null && node.right.elem.compareTo(elem) == 0 &&
node.parent != null && node.parent.right.elem.compareTo(node.elem) == 0) {
return leftRotate(node, node.parent, true);
}
// case 2: right-left
if (node.left != null && node.left.elem.compareTo(elem) == 0 &&
node.parent != null && node.parent.right.elem.compareTo(node.elem) == 0) {
node.right = rightRotate(node, node.parent, false);
return leftRotate(node, node.parent, true);
}
// case 3: left-left
if (node.left != null && node.left.elem.compareTo(elem) == 0 &&
node.parent != null && node.parent.left.elem.compareTo(node.elem) == 0) {
return rightRotate(node, node.parent, true);
}
// case 4: left-right
if (node.right != null && node.right.elem.compareTo(elem) == 0 &&
node.parent != null && node.parent.left.elem.compareTo(node.elem) == 0) {
node.left = leftRotate(node, node.parent, false);
return rightRotate(node, node.parent, true);
}
}
}
return node;
}
private RBNode<E> recoloring(RBNode<E> n, boolean isRoot) {
n.parent.left.color = Color.BLACK;
n.parent.right.color = Color.BLACK;
if (!isRoot) {
n.parent.color = Color.RED;
return n.parent;
} else return n;
}
private RBNode<E> leftRotate(RBNode<E> n, RBNode<E> pt, boolean changeColor) {
RBNode<E> pt_right = pt.right;
pt.right = pt_right.left;
if (pt.right != null) pt.right.parent = pt;
pt_right.parent = pt.parent;
if (pt.parent == null) root = pt_right;
else if (pt == pt.parent.left) pt.parent.left = pt_right;
else pt.parent.right = pt_right;
pt_right.left = pt;
pt.parent = pt_right;
// coloring
if (changeColor) {
pt.color = Color.RED;
n.color = Color.BLACK;
}
return n;
}
private RBNode<E> rightRotate(RBNode<E> n, RBNode<E> pt, boolean changeColor) {
RBNode<E> pt_left = pt.left;
pt.left = pt_left.right;
if (pt.left != null) pt.left.parent = pt;
pt_left.parent = pt.parent;
if (pt.parent == null) root = pt_left;
else if (pt == pt.parent.left) pt.parent.left = pt_left;
else pt.parent.right = pt_left;
pt_left.right = pt;
pt.parent = pt_left;
// coloring
if (changeColor) {
pt.color = Color.RED;
n.color = Color.BLACK;
}
return n;
}
public boolean find(E elem) {
return findHelper(root, elem);
}
private boolean findHelper(RBNode<E> node, E elem) {
if (node == null) return false;
if (node.elem.compareTo(elem) == 0) return true;
if (node.elem.compareTo(elem) > 0) return findHelper(node.left, elem);
else return findHelper(node.right, elem);
}
private class RBNode<E> {
private E elem;
private Color color;
private RBNode<E> left, right, parent;
public RBNode(E elem, RBNode<E> parent, Color color) {
this.elem = elem;
this.parent = parent;
this.color = color;
}
}
private enum Color {
RED, BLACK
}
public static void main(String[] args) {
RedBlackTree<Integer> rb = new RedBlackTree<>();
rb.insert(6);
rb.insert(-3);
rb.insert(10);
rb.insert(15);
rb.insert(20);
}
}