rb_node_t * rbt_pre(rb_node_t * z)
{
if(z == NIL_NODE){
return z;
}
if(l(z) != NIL_NODE){
return rbt_max(l(z));
}
rb_node_t *x = z;
while(p(x) != NIL_NODE && x == l(p(x))){
x = p(x);
}
return p(x);
}
rbnode_t * rbt_predecessor(rbtree_t *T,rbnode_t *x)
{
rbnode_t *y;
if (x->l != &T->nil) {
y = rbt_max(T,x->l);
} else {
y = x->p;
while ((y != &T->nil) && (y->l == x)) {
x = y;
y = x->p;
}
if (y == &T->nil) {
y = 0;
}
}
return y;
}
