(Easy) Reverse linked list LeetCode

发布时间：2020-12-14 00:08:16 所属栏目：Linux 来源：网络整理

导读：Description: 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? Accepted 661,364 Submissions 1,172,734 ?

Description:

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?

Accepted

661,364

Submissions

1,172,734

Solution:

　　Explanation:

Iterative Method

Initialize three pointers prev as NULL,curr as head and next as NULL.

Iterate trough the linked list. In loop,do following.
// Before changing next of current,
// store next node
next = curr->next
// Now change next of current
// This is where actual reversing happens
curr->next = prev

// Move prev and curr one step forward
prev = curr
curr = next

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        
        ListNode prev =null,curr = head,next = null;
        
        
        while(curr!=null){
            
            
             next = curr.next; 
            
             curr.next = prev;
            
             prev = curr; 
            
             curr = next;
        }
        
        
        return prev;
        
        
    }
}

（编辑：李大同）

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