leetcode/code/lc206.java at master · mJackie/leetcode · GitHub

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package code;

* 206. Reverse Linked List

* 题意：链表反转

* 难度：Easy

* 分类：Linked List

* 思路：2中方法：设置一个快走一步的快指针，注意赋值操作顺序。还有一种递归的方法。

* Tips：递归的方法有点绕，多看下

* lc25, lc206

public class lc206 {

public class ListNode {

int val;

ListNode next;

ListNode(int x) { val = x; }

}

public ListNode reverseList(ListNode head) {

ListNode pre = null; //头结点变尾节点，指向null

while(head!=null){

ListNode next = head.next;

head.next = pre;

pre = head;

head = next;

}

return pre;

}

public ListNode reverseList2(ListNode head) { //递归

return reverseListInt(head, null);

}

private ListNode reverseListInt(ListNode head, ListNode pre) {

if (head == null)

return pre;

ListNode next = head.next;

head.next = pre;

return reverseListInt(next, head); //尾递归，操作已经完成，最后返回最后结果罢了

}

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