206 Reverse Linked List

Reverse a singly linked list.

 

解法： linked list 最典型的题型之一。

 

public ListNode ReverseList(ListNode head) {
       var sentinel = new ListNode(0);
       
       var dummy = new ListNode(0);
       dummy.next = head;
       while(dummy.next != null)
       {
           dummy.next = head.next;
           var temp = sentinel.next;
           sentinel.next = head;
           sentinel.next.next = temp;
       }
       return sentinel.next;
    }

思路相同，也可以不用哨兵：

 public ListNode ReverseList(ListNode head) {
       if(head == null) return head;
       ListNode nextNode = null;
       ListNode newHead = null;
       while(head != null)
       {
           nextNode = head.next;
           head.next = newHead;
           newHead = head;
           head = nextNode;
       }
       return newHead;
    }