BST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在BST中迭代插入元素。关于如何解决迭代方法，我不需要答案。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 
} 

被称为像：

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