Question brushing record ---- reverse the linked list (reverse the whole linked list)

Catalog

Title Description ： Given a linked list , Invert and return to the new header node

iteration ：

Two pointers ,pre and cur,cur Traverse the linked list instead of the head node , In the process next Record cur.next

recursive ：

recursive ： Reverse from back to front

hold head.next Later nodes are treated as a node

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Title Description ： Given a linked list , Invert and return to the new header node

iteration ：

Two pointers ,pre and cur,cur Traverse the linked list instead of the head node , In the process next Record cur.next

ListNode reverse(ListNode head) {
    ListNode pre = null, cur = head;
    while (cur != null) {
        ListNode next = cur.next;// Record the next node 
        cur.next = pre;// Change the direction of the first node 
        pre = cur;// The predecessor node is updated to the current node 
        cur = next;// Update node backward 

    }
    return pre;
}

recursive ：

 public ListNode reverseList(ListNode head) {
        return reverse(null, head);
    }

    private ListNode reverse(ListNode prev, ListNode cur) {
        if (cur == null) {
            return prev;
        }
        ListNode temp = null;
        temp = cur.next;//  Save the next node first 
        cur.next = prev;//  reverse 
        //  to update prev、cur Location 
        // prev = cur;
        // cur = temp;
        return reverse(cur, temp);
    }

recursive ： Reverse from back to front

hold head.next Later nodes are treated as a node

    ListNode reverseList(ListNode head) {
        //  Edge condition judgment 
        if(head == null) return null;
        if (head.next == null) return head;
        
        //  Recursively call , Flip the second node and start the subsequent linked list 
        ListNode last = reverseList(head.next);
        //  Turn the direction between the head node and the second node 
        head.next.next = head;
        //  At this time  head  The node is the tail node ,next  Need to point to  NULL
        head.next = null;
        return last;
    }