Simple Objective-C AVL Tree

AVLTree.h

//
//  AVLTree.h
//  AVLTree-ObjC
//
//  Created by Arnaud Schildknecht on 17/06/15.
//  Copyright (c) 2015 Arnaud Schildknecht. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface AVLTree : NSObject

@property (strong, nonatomic) id        data;
@property (strong, nonatomic) AVLTree   *right;
@property (strong, nonatomic) AVLTree   *left;
@property (nonatomic) int               count;

- (void)addValue: (id)value;
- (NSArray*)inOrder;
- (NSArray*)preOrder;
- (NSArray*)postOrder;

@end

AVLTree.m

//
//  AVLTree.m
//  AVLTree-ObjC
//
//  Created by Arnaud Schildknecht on 17/06/15.
//  Copyright (c) 2015 Arnaud Schildknecht. All rights reserved.
//

#import "AVLTree.h"

@implementation AVLTree

- (id)init
{
  self = [super init];
  if (self) {
    _count = 0;
  }
  return self;
}

- (void)addValue: (id)value {
  if (!self.data)
    self.data = value;
  else
    [self add:value];
  ++_count;
}

- (void)add: (id)value {
  if (value < self.data) {
    if (self.left)
      [self.left addValue:value];
    else {
      self.left = [[AVLTree alloc] init];
      
      [self.left setData:value];
    }
  }
  else {
    if (self.right)
      [self.right addValue:value];
    else {
      self.right = [[AVLTree alloc] init];
      
      [self.right setData:value];
    }
  }
}

- (NSArray*)inOrder {
  NSMutableArray *datas = [[NSMutableArray alloc] init];
  
  [self inOrder:self datas:datas];
  return datas;
}

- (void)inOrder: (AVLTree*)root datas:(NSMutableArray*)datas {
  if (root) {
    [self inOrder:root.left datas:datas];
    [datas addObject:root.data];
    [self inOrder:root.right datas:datas];
  }
}

- (NSArray*)preOrder {
  NSMutableArray *datas = [[NSMutableArray alloc] init];
  
  [self preOrder:self datas:datas];
  return datas;
}

- (void)preOrder: (AVLTree*)root datas:(NSMutableArray*)datas {
  if (root) {
    [datas addObject:root.data];
    [self preOrder:root.left datas:datas];
    [self preOrder:root.right datas:datas];
  }
}

- (NSArray*)postOrder {
  NSMutableArray *datas = [[NSMutableArray alloc] init];
  
  [self postOrder:self datas:datas];
  return datas;
}

- (void)postOrder: (AVLTree*)root datas:(NSMutableArray*)datas {
  if (root) {
    [self postOrder:root.left datas:datas];
    [self postOrder:root.right datas:datas];
    [datas addObject:root.data];
  }
}

@end