《LeetCode力扣练习》代码随想录——链表（反转链表---Java）

《LeetCode力扣练习》代码随想录——链表（反转链表—Java）

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刷题思路来源于 代码随想录

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206. 反转链表

• 双指针法

  /**
   * Definition for singly-linked list.
   * public class ListNode {
   *     int val;
   *     ListNode next;
   *     ListNode() {}
   *     ListNode(int val) { this.val = val; }
   *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
   * }
   */
  class Solution {
      public ListNode reverseList(ListNode head) {
  
          if(head==null){
              return null;
          }
  
          ListNode slow=null;
          ListNode fast=head;
  
          while(fast!=null){
  
              ListNode temp=fast.next;
              fast.next=slow;
              slow=fast;
              fast=temp;
  
          }
  
          return slow;
  
      }
  }
  

• 递归法

  /**
   * Definition for singly-linked list.
   * public class ListNode {
   *     int val;
   *     ListNode next;
   *     ListNode() {}
   *     ListNode(int val) { this.val = val; }
   *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
   * }
   */
  class Solution {
      public ListNode reverseList(ListNode head) {
  
          if(head==null){
              return null;
          }
  
          return reverse(null,head);
  
      }
  
      public ListNode reverse(ListNode slow,ListNode fast){
  
          if(fast==null){
              return slow;
          }
  
          ListNode temp=fast.next;
          fast.next=slow;
  
          return reverse(fast,temp);
  
      }
  }
  

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