Delete Kth node from doubly linked list

With node (prev, info, next) and start pointing to the first node:

Algorithm DELETE_K(start, k)

1. If start == NULL print "underflow" and stop.
2. Set p = start; repeat k-1 times: p = p->next; if p becomes NULL print "invalid position" and stop.
3. If p->prev != NULL then p->prev->next = p->next; else start = p->next.
4. If p->next != NULL then p->next->prev = p->prev.
5. x = p->info; free(p); return x.

Before: [a] <-> [p(K)] <-> [b]
After : [a] <-> [b]