206. Reverse Linked List.md

206. Reverse Linked List

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Difficulty : Easy

Related Topics : LinkedList

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Reverse a singly linked list.

Example:

Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL

Follow up:

• A linked list can be reversed either iteratively or recursively. Could you implement both?

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Solution

• mine
  • Java
    • Runtime: 0 ms, faster than 100.00%, Memory Usage: 38.7 MB, less than 6.69% of Java online submissions

      // O(N)time
      // O(1)space
      public ListNode reverseList(ListNode head) {
          ListNode res = null;
          while(head != null){
              ListNode t = head;
              head =  head.next;
              t.next = res;
              res = t;
          }
          return res;
      }
      

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