diff --git a/链表/10. K 个一组翻转链表.md b/链表/10. K 个一组翻转链表.md new file mode 100644 index 0000000..0a4d29c --- /dev/null +++ b/链表/10. K 个一组翻转链表.md @@ -0,0 +1,101 @@ +# K 个一组翻转链表 + +## 题目 + +给你链表的头节点 head ,每 k 个节点一组进行翻转,请你返回修改后的链表。 + +k 是一个正整数,它的值小于或等于链表的长度。如果节点总数不是 k 的整数倍,那么请将最后剩余的节点保持原有顺序。 + +你不能只是单纯的改变节点内部的值,而是需要实际进行节点交换。 + + + +示例 1: + + +输入:head = [1,2,3,4,5], k = 2 +输出:[2,1,4,3,5] +示例 2: + + + +输入:head = [1,2,3,4,5], k = 3 +输出:[3,2,1,4,5] + + +提示: +链表中的节点数目为 n +1 <= k <= n <= 5000 +0 <= Node.val <= 1000 + + +进阶:你可以设计一个只用 O(1) 额外内存空间的算法解决此问题吗? + + +## 思路 + +- 分解 + - 判定 + - 区域翻转 + +## 代码 + +```java +/** + * 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 reverseKGroup(ListNode head, int k) { + // Init: DummyHead, begin, end + ListNode dummyHead = new ListNode(-1); + dummyHead.next = head; + ListNode begin = dummyHead; + ListNode end = dummyHead; + // Traverse 1: end -> null + while (end.next != null) { + // Traverse 2: Find K + int cnt = 0; + while (end != null && cnt < k) { + end = end.next; + cnt ++; + } + if (end == null) { + break; + } + + // Begin [pA...... end ] pB + // Begin [end...... pA ] pB + ListNode pA = begin.next; + ListNode pB = end.next; + // Operation + end.next = null; + reverse(pA); + begin.next = end; + pA.next = pB; + + begin = end = pA; + } + + return dummyHead.next; + } + + void reverse(ListNode head) { + ListNode dummyHead = new ListNode(-1); + ListNode cur = head; + while (cur != null) { + // dummyHead -> new -> others + ListNode tmp = dummyHead.next; + dummyHead.next = cur; + cur = cur.next; + dummyHead.next.next = tmp; + } + } +} +``` \ No newline at end of file