BST的插入迭代方法（C）

Question

我已经找到了递归方法，但我似乎无法弄清楚如何迭代地在BST中插入元素。关于如何解决迭代方法，我不需要回答一点方向。谢谢！

static NODE * insert(NODE *r, int x)  //recursive approach
{
    NODE *leaf;
    if(r == NULL)
    {
      leaf = malloc(sizeof(NODE));
      leaf->left = NULL;
      leaf->right = NULL;
      leaf->val = x;
      return leaf;
    }

    if(r->val == x)
        return r;

    if(x < r->val)
    {
        r->left = insert(r->left, x);
        return r;
    }
    else 
    {
        r->right = insert(r->right, x);
        return r;
    }
}

static NODE *insert_i(NODE *r, int x) //iterative approach
{
    NODE *leaf;

    if(r == NULL)
    {
      leaf = malloc(sizeof(NODE));
      leaf->left = NULL;
      leaf->right = NULL;
      leaf->val = x;
      return leaf;
    }


}

Answer 1

static NODE * insert_i(NODE **rr, int x)
{
  while (*rr) {
    if((*rr)->val == x) break;
    rr = (x < (*rr)->val) ? &(*rr)->left : &(*rr)->right;
    }

  if(*r) return *r; /* duplicate */

  (*rr) = malloc(sizeof **r);
  (*rr)->left = NULL;
  (*rr)->right = NULL;
  (*rr)->val = x;
  return *rr
}

被称为：

NODE *root=NULL, pp;
pp = insert_i( &root, 1234);