206. 反轉(zhuǎn)一個(gè)單鏈表。

示例:
輸入: 1->2->3->4->5->NULL
輸出: 5->4->3->2->1->NULL

/**
 * 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 loopNode = head;
        ListNode reverseNode = null;

        while (loopNode != null) {
            ListNode temp = loopNode.next;
            loopNode.next = reverseNode;
            reverseNode = loopNode;
            loopNode = temp;
        }
        return reverseNode;
    }
}

復(fù)雜度分析

時(shí)間復(fù)雜度 : O(n)
空間復(fù)雜度 : O(1)