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Given a LinkedList, reverse it in place.

Link

Approaches

O(n) time. O(1) space.

Similar to swapping two numbers. Start with prev as null and current and keep swapping next. Return prev because that’s the last value.

[image]

    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode current = head;
        
        while(current!=null){
            ListNode tempCurrent = current.next;
            
            current.next = prev;
            prev = current;
            
            current = tempCurrent;
        }
        return prev;        
    }