Maintain slow and fast pointers advancing at different speeds

slow = head; fast = head; while(fast && fast.next){ slow = slow.next; fast = fast.next.next; }

Iteratively reverse next pointers to flip list direction

prev=null; cur=head; while(cur){ nxt=cur.next; cur.next=prev; prev=cur; cur=nxt; }

Select smaller head from two sorted lists repeatedly

while(a && b){ if(a.val<b.val){ tail.next=a; a=a.next; } else { tail.next=b; b=b.next;} tail=tail.next; }

After meet, reset one pointer to head and move both 1 step to find entry

while(fast&&fast.next){ slow=slow.next; fast=fast.next.next; if(slow===fast){ slow=head; while(slow!==fast){ slow=slow.next; fast=fast.next;} break; }}

Divide list into two based on condition, then recombine

before/after lists; iterate nodes; append to bucket; join

Use middle discovery then modify second half then reconnect

mid via slow/fast; reverse second; weave first & reversed