Likou 206_Reverse Linked List

Reverse linked list

Description: Reverse a singly linked list.

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

This article uses an iterative method to reverse the linked list. The
basic idea: When traversing, point the next node of the current node to the previous node
. Problems that occur:

• Due to the one-way link list, the address of the previous node is unknown
• If you change the next value of the current node, the address of the subsequent node will be lost

Solution:

• Use prev and cur pointers to point to the predecessor and current node respectively
• Store the address of the subsequent node in nextTemp

The process is shown in the figure below (only three nodes are listed) and the

code is as follows:

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode cur = head;
        while(cur != null){
            ListNode nextTemp = cur.next;
            cur.next = prev;
            prev = cur;
            cur = nextTemp;
        }
        return prev;
    }
}

Complexity analysis:
Time complexity: O(n)
Space complexity: O(1)