Question

describe a fast recursive algorithm for reversing a singly linked list l, so that the ordering of the nodes becomes opposite of what it was before

Answer 1

struct Node {

int data;

Node *next;

};

Node *reverse_list(Node *head) {

if (head == nullptr || head->next == nullptr) {

return head;

}

Node *new_head = reverse_list(head->next);

head->next->next = head;

head->next = nullptr;

return new_head;

}

Step-by-step explanation:

The reverse_list function takes a pointer to the head of the list as input and returns a pointer to the new head of the reversed list. The function works as follows:

1. If the list is empty or has only one node, then it returns the head, since the list is already reversed.
2. Otherwise, it calls itself recursively with the next node in the list.
3. After the recursive call returns, the current node's next pointer is updated to point to the previous node, effectively reversing the direction of the link.
4. Finally, the function returns the new head of the reversed list.