二叉搜索树的java实现

public class BinarySearchTree<T extends Comparable> {

	private static class Entity<T extends Comparable> {
		private T node = null;
		private Entity<T> parent = null;
		private Entity<T> left = null;
		private Entity<T> right = null;

		public T getNode() {
			return node;
		}
		public void setNode(T node) {
			this.node = node;
		}
		public Entity<T> getParent() {
			return parent;
		}
		public void setParent(Entity<T> parent) {
			this.parent = parent;
		}
		public Entity<T> getLeft() {
			return left;
		}
		public void setLeft(Entity<T> left) {
			this.left = left;
		}
		public Entity<T> getRight() {
			return right;
		}
		public void setRight(Entity<T> right) {
			this.right = right;
		}
	}

	private Entity<T> head = null;

	public void append(T node) {
		Entity<T> entity = new Entity<T>();
		entity.setNode(node);
		if(head == null) {
			head = entity;
		} else {
			Entity<T> pointer = head;
			while(pointer != null) {
				if(pointer.getNode().compareTo(entity.getNode()) > 0) {
					if(pointer.getLeft() == null) {
						pointer.setLeft(entity);
						entity.setParent(pointer);

						break;
					}

					pointer = pointer.getLeft();
				} else{
					if(pointer.getRight() == null) {
						pointer.setRight(entity);
						entity.setParent(pointer);

						break;
					}

					pointer = pointer.getRight();
				}
			}
		}
	}

	public boolean remove(T node) {
		if(head == null) return false;

		Entity<T> pointer = head;
		while(pointer != null) {
			if(pointer.getNode().compareTo(node) > 0) {
				pointer = pointer.getLeft();
			} else if(pointer.getNode().compareTo(node) < 0) {
				pointer = pointer.getRight();
			} else {
				removeNode(pointer);
				return true;
			}
		}

		return false;
	}

	private void removeNode(Entity<T> pointer) {
		Entity<T> cursor = pointer;

		while(true) {
			if(cursor.getLeft() != null) {
				cursor = cursor.getLeft();
			} else if (cursor.getRight() != null) {
				cursor = cursor.getRight();
			} else {
				break;
			}
		}

		Entity<T> parent = cursor.getParent();
		if(parent.getNode().compareTo(cursor.getNode()) > 0) {
			parent.setLeft(null);
		} else {
			parent.setRight(null);
		}

		cursor.setParent(null);

		pointer.setNode(cursor.getNode());

		rebuild(pointer);
	}

	private void rebuild(Entity<T> pointer) {
		if(pointer != null) {
			if(pointer.getLeft() != null) {
				if(pointer.getNode().compareTo(pointer.getLeft().getNode()) < 0) {
					T node = pointer.getNode();

					pointer.setNode(pointer.getLeft().getNode());

					pointer.getLeft().setNode(node);
				}
			} 

			if(pointer.getRight() != null) {
				if(pointer.getNode().compareTo(pointer.getRight().getNode()) > 0) {
					T node = pointer.getNode();

					pointer.setNode(pointer.getRight().getNode());

					pointer.getLeft().setNode(node);
				}
			}

			if(pointer.getLeft() != null) {
				rebuild(pointer.getLeft());
			}

			if(pointer.getRight() != null) {
				rebuild(pointer.getRight());
			}
		}
	}

	public void print() {
		treeWalk(head);
		System.out.println();
	}

	private void treeWalk(Entity<T> entity) {
		if(entity != null) {
			treeWalk(entity.getLeft());
			System.out.print(entity.getNode() + " ");
			treeWalk(entity.getRight());
		}
	}

	public T search(T node) {
		T result = binarySearch(head, node);

		return result;
	}

	public T search2(T node) {
		Entity<T> top = head;

		while(top != null) {
			if(node.equals(top.getNode())) {
				return top.getNode();
			} 

			if(node.compareTo(top.getNode()) > 0) {
				top = top.getRight();
			} else {
				top = top.getLeft();
			}
		}

		return null;
	}

	public T maximun() {
		Entity<T> top = head;
		while(top.getRight() != null) {
			top = top.getRight();
		}

		return top.getNode();
	}

	public T minimum() {
		Entity<T> top = head;
		while(top.getLeft() != null) {
			top = top.getLeft();
		}

		return top.getNode();
	}

	private T binarySearch(Entity<T> top, T node) {
		if(top == null) return null;

		if(node.equals(top.getNode())) {
			return top.getNode();
		}
		if(node.compareTo(top.getNode()) > 0) {
			return binarySearch(top.getRight(), node);
		} else {
			return binarySearch(top.getLeft(), node);
		}
	}

	public static void main(String[] args) {
		BinarySearchTree<Integer> tree = new BinarySearchTree<Integer>();

		tree.append(10);
		tree.append(5);
		tree.append(13);
		tree.append(6);
		tree.append(4);
		tree.append(18);
		tree.append(11);
		tree.append(9);
		tree.append(16);
		tree.append(7);
		tree.append(2);

		tree.print();

		tree.remove(5);
		tree.remove(18);

		tree.print();

		System.out.println(tree.search(18));
	}

}