需要关于Objective-C中二进制搜索树实现的方向

I have a partial implementation of a binary tree that doesn't work properly. I believe I am missing fundamental knowledge about struct memory management in objective-c but not sure what it is(besides malloc). When I try to create a new tree node based on a struct I get

我部分实现了无法正常工作的二叉树。我相信我在objective-c中缺少关于结构内存管理的基础知识但不确定它是什么（除了malloc）。当我尝试基于我得到的结构创建新的树节点时

Thread 1: EXC_BAD_ACCESS (code=1, address=0x0)

线程1：EXC_BAD_ACCESS（代码= 1，地址= 0x0）

which led me to believe I didn't create a memory location for this struct pointer. What is the proper way of doing this in Objective-C? (Code in below)

这让我相信我没有为这个结构指针创建一个内存位置。在Objective-C中执行此操作的正确方法是什么？（下面的代码）

Thank you for taking the time to respond. The code seems correct from the logic perspective so not sure what the issue is here.

感谢您抽出宝贵时间作出回应。从逻辑角度来看，代码似乎是正确的，所以不确定这里的问题是什么。

EDIT I've modified the source code based on @trungduc 's response. But now I am getting a stack overflow in the printDescription method issue:

编辑我根据@trungduc的响应修改了源代码。但是现在我在printDescription方法问题中遇到了堆栈溢出：

Thread 1: EXC_BAD_ACCESS (code=2, address=0x7ffeef3fffe8) // on line [self printDescription:root.left];

PS. I did see this question but didn't help. I also saw this repo but I am not sure happy with some of the implementation details so I ended up not following it. Does anyone know any good guides/tutorials on how to do trees and graphs in Objective-C?

PS。我确实看到了这个问题，但没有帮助。我也看到了这个回购，但我不确定对某些实现细节感到满意所以我最终没有关注它。有没有人知道如何在Objective-C中做树和图的好指南/教程？

Main.m

的main.m

#import <Foundation/Foundation.h>

// BSTNode is an Objective-C class
@interface BSTNode : NSObject

@property (nonatomic, assign) int data;
@property (nonatomic, strong) BSTNode *left;
@property (nonatomic, strong) BSTNode *right;

@end

@implementation BSTNode

@end

@interface BST: NSObject

- (BSTNode *)insertNode:(BSTNode *)root withData:(int)data;
- (void)printDescription:(BSTNode *)root;

@end

@implementation BST

- (BSTNode *)initializeTreeNode {
    // By default, |data| is 0, |left| is nil, |right| is nil
    return [[BSTNode alloc] init];
}

- (BSTNode *)insertNode:(BSTNode *)root withData:(int)data {
    if(!root) {
        root = [self initializeTreeNode];
        root.data = data;
    } else if (root.data >= data) {
        root.left = [self insertNode:root.left withData:data];
    } else {
        root.right = [self insertNode:root.right withData:data];
    }

    return root;
}

- (void)printDescription:(BSTNode *)root {
    // in order left - root - right
    [self printDescription:root.left];
    NSLog(@"%d",root.data);
    [self printDescription:root.right];
}

@end

and inside the main method:

并在主方法内：

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        BST *bst = [[BST alloc] init];;
        BSTNode *root = [[BSTNode alloc]init];
        [bst insertNode:root withData:20];
        [bst insertNode:root withData:15];
        [bst insertNode:root withData:25];
        [bst printDescription:root];
   }
    return 0;
}

1 个解决方案

#1

You got crash because you called node->data while node is NULL.

您因为在节点为NULL时调用了node-> data而崩溃了。

In this case, I suggest to define BSTNode as an Objective-C class. You can try my code below.

在这种情况下，我建议将BSTNode定义为Objective-C类。您可以在下面尝试我的代码。

// BSTNode is an Objective-C class
@interface BSTNode : NSObject

@property (nonatomic, assign) int data;
@property (nonatomic, strong) BSTNode *left;
@property (nonatomic, strong) BSTNode *right;

@end

@implementation BSTNode

@end

@interface BST: NSObject

- (BSTNode *)insertNode:(BSTNode *)root withData:(int)data;
- (void)printDescription:(BSTNode *)root;

@end

@implementation BST

- (BSTNode *)initializeTreeNode {
  // By default, |data| is 0, |left| is nil, |right| is nil
  return [[BSTNode alloc] init];
}

- (BSTNode *)insertNode:(BSTNode *)root withData:(int)data {
  if(!root) {
    root = [self initializeTreeNode];
    root.data = data;
  } else if (root.data >= data) {
    root.left = [self insertNode:root.left withData:data];
  } else {
    root.right = [self insertNode:root.right withData:data];
  }

  return root;
}

- (void)printDescription:(BSTNode *)root {
  if (!root) {
      return;
  }

  // in order left - root - right
  [self printDescription:root.left];
  NSLog(@"%d",root.data);
  [self printDescription:root.right];
}

@end

#1