Linked List — Pointer Surgery

Redraw next pointers carefully; draw on paper first.

When to use this

Reverse
Merge sorted
Cycle (Floyd)

C++ template

ListNode* prev = nullptr;
ListNode* cur = head;
while (cur) {
    ListNode* nxt = cur->next;
    cur->next = prev;
    prev = cur;
    cur = nxt;
}
return prev;

Dry run

1→2→3 reverse → 3→2→1.

Pitfalls

Losing next
No dummy on merge
Cycle entry mistakes

Say this in the interview

prev/cur/next so I never lose the list.

Problems in this topic (3)

Each opens teach-first (animated when available), then the code panel.