面试经典-旋转链表

旋转链表

题目

61. 旋转链表

给你一个链表的头节点 head ，旋转链表，将链表每个节点向右移动 k 个位置。

示例 1：

输入：head = [1,2,3,4,5], k = 2
输出：[4,5,1,2,3]

示例 2：

输入：head = [0,1,2], k = 4
输出：[2,0,1]

提示：

• 链表中节点的数目在范围 [0, 500] 内
• -100 <= Node.val <= 100
• 0 <= k <= 2 * 109

题解

此题有点难，适合二刷

public class RotateRight {

    public static void main(String[] args) {
        ListNode node1 = new ListNode(1);
        node1.next = new ListNode(2);
        node1.next.next = new ListNode(3);
        node1.next.next.next = new ListNode(4);
        node1.next.next.next.next = new ListNode(5);
        ListNode node = rotateRight(node1, 2);
        System.out.println("===================");
        while (node != null) {
            System.out.println(node.val);
            node = node.next;
        }
    }


    public static ListNode rotateRight(ListNode head, int k) {
        if (head == null || head.next == null) {
            return head;
        }
        int n = getLength(new ListNode(0, head)) - 1;
        // 将链表转为环形链表
        ListNode iter = head;
        while (iter.next != null) {
            iter = iter.next;
        }
        iter.next = head;
        for (int i = 0; i <  n - k % n; i++) {
            iter = iter.next;
        }
        ListNode newHead = iter.next;
        iter.next = null;
        return newHead;
    }

    public static ListNode rotateRight2(ListNode head, int k) {
        if (k == 0 || head == null || head.next == null) {
            return head;
        }
        int n = 1;
        ListNode iter = head;
        while (iter.next != null) {
            iter = iter.next;
            n++;
        }
        int add = n - k % n;
        if (add == n) {
            return head;
        }
        iter.next = head;
        while (add-- > 0) {
            iter = iter.next;
        }
        ListNode ret = iter.next;
        iter.next = null;
        return ret;
    }


    public static int getLength(ListNode head) {
        int length = 0;
        while (head != null) {
            ++length;
            head = head.next;
        }
        return length;
    }

}
class ListNode {
    int val;
    ListNode next;

    ListNode() {
    }

    ListNode(int val) {
        this.val = val;
    }

    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
}