tsearch

void * tsearch(const void *vkey, void **vrootp,

    int (*compar)(const void *, const void *))

#include <search.h>
#include <stdlib.h>

typedef struct node_t {
    char	  *key;
    struct node_t *left, *right;
} node;

/* find or insert datum into search tree */
void *
tsearch(const void *vkey, void **vrootp,
    int (*compar)(const void *, const void *))
{
    node *q;
    char *key = (char *)vkey;
    node **rootp = (node **)vrootp;

    if (rootp == (struct node_t **)0)
	return ((void *)0);
    while (*rootp != (struct node_t *)0) {	/* Knuth's T1: */
	int r;

	if ((r = (*compar)(key, (*rootp)->key)) == 0)	/* T2: */
	    return ((void *)*rootp);		/* we found it! */
	rootp = (r < 0) ?
	    &(*rootp)->left :		/* T3: follow left branch */
	    &(*rootp)->right;		/* T4: follow right branch */
    }
    q = (node *) malloc(sizeof(node));	/* T5: key not found */
    if (q != (struct node_t *)0) {	/* make new node */
	*rootp = q;			/* link new node to old */
	q->key = key;			/* initialize new node */
	q->left = q->right = (struct node_t *)0;
    }
    return ((void *)q);
}

/* delete node with given key */
void *
tdelete(const void *vkey, void **vrootp,
    int (*compar)(const void *, const void *))
{
    node **rootp = (node **)vrootp;
    char *key = (char *)vkey;
    node *p;
    node *q;
    node *r;
    int cmp;

    if (rootp == (struct node_t **)0 || (p = *rootp) == (struct node_t *)0)
	return ((struct node_t *)0);
    while ((cmp = (*compar)(key, (*rootp)->key)) != 0) {
	p = *rootp;
	rootp = (cmp < 0) ?
	    &(*rootp)->left :		/* follow left branch */
	    &(*rootp)->right;		/* follow right branch */
	if (*rootp == (struct node_t *)0)
	    return ((void *)0);		/* key not found */
    }
    r = (*rootp)->right;			/* D1: */
    if ((q = (*rootp)->left) == (struct node_t *)0)	/* Left (struct node_t *)0? */
	q = r;
    else if (r != (struct node_t *)0) {		/* Right link is null? */
	if (r->left == (struct node_t *)0) {	/* D2: Find successor */
	    r->left = q;
	    q = r;
	} else {			/* D3: Find (struct node_t *)0 link */
	    for (q = r->left; q->left != (struct node_t *)0; q = r->left)
		r = q;
	    r->left = q->right;
	    q->left = (*rootp)->left;
	    q->right = (*rootp)->right;
	}
    }
    if (p == *rootp)
        p = q;
    free((struct node_t *) *rootp);	/* D4: Free node */
    *rootp = q;				/* link parent to new node */
    return(p);
}

/* Walk the nodes of a tree */
static void
trecurse(node *root, void (*action)(const void *, VISIT, int), int level)
{
    if (root->left == (struct node_t *)0 && root->right == (struct node_t *)0)
	(*action)(root, leaf, level);
    else {
	(*action)(root, preorder, level);
	if (root->left != (struct node_t *)0)
	    trecurse(root->left, action, level + 1);
	(*action)(root, postorder, level);
	if (root->right != (struct node_t *)0)
	    trecurse(root->right, action, level + 1);
	(*action)(root, endorder, level);
    }
}

/* Walk the nodes of a tree */
void
twalk(const void *vroot, void (*action)(const void *, VISIT, int))
{
    node *root = (node *)vroot;

    if (root != (node *)0 && action != (void (*)(const void *, VISIT, int))0)
	trecurse(root, action, 0);
}