TADM2E 3.2

typedef struct Node {
    char *value;
    struct Node *next;
} Node;

int reverse(Node **head) {
    Node *curr, *prev, *next;

    if (!head || !(*head)) {
        return 0;
    }

    curr = *head;
    prev = NULL;
    next = NULL;

    while (curr) {
        next =  curr->next;
        curr->next = prev;
        prev = curr;
        curr = next;
    }

    *head = prev;

    return 1;
}

---

In Java

class ListNode {
    int val;
    ListNode next;

    ListNode(final int x) {
        val = x;
        next = null;
    }
}

public class LinkedList {
    ListNode head;

    public LinkedList() {
        head = null;
    }

    public void prepend(final int in) {
        final ListNode data = new ListNode(in);
        data.next = head;
        head = data;
    }

    public void appendToList(final int in) {
        final ListNode data = new ListNode(in);
        ListNode current = head;
        if (head == null) {
            head = data;
            return;
        }
        while (current.next != null) {
            current = current.next;
        }
        current.next = data;
    }

    public void printList(final ListNode head) {
        ListNode current = head;
        while (current != null) {
            System.out.print(current.val + " -> ");
            current = current.next;
        }
        System.out.println();
    }
    
    public ListNode reverseList(final ListNode node) {
        //what if 0 node in list
        if (node == null) {
            return null;
        }
        //what if 1 node in list
        if (node.next == null) {
            return node;
        }
        //what if multiple nodes.divide into two parts . reverse second part recursively and in end point second.next to first 
        final ListNode secondElem = node.next;
        node.next = null;
        final ListNode reverseRest = reverseList(secondElem);
        secondElem.next = node;
        return reverseRest;
    }
    
    public static void main(final String[] args) {
        final LinkedList linkedList = new LinkedList();
        linkedList.appendToList(12);
        linkedList.appendToList(13);
        linkedList.appendToList(14);
        linkedList.appendToList(15);
        linkedList.printList(linkedList.head);
        final ListNode head = linkedList.reverseList(linkedList.head);
        linkedList.printList(head);
    }

}

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