二叉搜身树（BST）的插入、删除、查找、遍历

#include <stdio.h>
#include <stdlib.h>

typedef struct node
{
int           id;
struct node   *left;
struct node   *right;
} node;

node *find(int id, node *root)
{
if (root == NULL)
return (NULL);

if (id < root->id)
return (find(id, root->left));
else if (id > root->id)
return (find(id, root->right));
else
return root;
}

node *findmin(node *root)
{
if (root == NULL)
return (NULL);

if (root->left == NULL)
return (root);
else
return (findmin(root->left));
}

node *insert(int id, node *root)
{
if (root == NULL)
{
root = malloc(sizeof(node));
if (root == NULL)
{
printf("out of memory\n");
return (NULL);
}
root->id = id;
root->left = root->right = NULL;
}
else if (id < root->id)
{
root->left = insert(id, root->left);
}
else if(id > root->id)
{
root->right = insert(id, root->right);
}

return (root);
}

node *delete(int id, node *root)
{
node  *tmp;

if (root == NULL)
printf("not found");
else if (id < root->id)
root->left = delete(id, root->left);
else if (id > root->id)
root->right = delete(id, root->right);
else
{
if (root->left && root->right)
{
tmp = findmin(root->right);
root->id = tmp->id;
root->right = delete(root->id, root->right);
}
else /* one or zero children */
{
tmp = root;
if (root->left == NULL)
root = root->right;
else if (root->right == NULL)
root = root->left;
free(tmp);
}
}

return root;
}

oid retrieve(node *root) // preorder
{
if (root)
{
printf("%d ", root->id);
retrieve(root->left);
retrieve(root->right);
}
}

void inorder(node *root) // inorder
{
if (root)
{
inorder(root->left);
printf("%d ", root->id);
inorder(root->right);
}
}

void postorder(node *root) // postorder
{
if (root)
{
postorder(root->left);
postorder(root->right);
printf("%d ", root->id);
}
}