leetcode刷题记录 3

 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class  {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode fast = head;
        ListNode slow = head;

        for (int i = 0; i < n; i++) {
            fast = fast.next;
        }

        if (fast == null) {
            return head.next;
        }

        while (fast.next != null) {
            fast = fast.next;
            slow = slow.next;
        }
        slow.next = slow.next.next;

        return head;
    }
}

 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class  {
    public ListNode swapPairs(ListNode head) {
        ListNode p = head;
        while (p != null && p.next != null) {
            int temp = p.val;
            p.val = p.next.val;
            p.next.val = temp;
            p = p.next.next;
        }
        return head;
    }
}

 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class  {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null)
            return head;
        
        ListNode fakeHead = new ListNode(0);
        fakeHead.next = head;
        ListNode fast = fakeHead;
        ListNode slow = fakeHead;
        
        int len = 0;
        ListNode p = head;
        while(p != null) {
            p = p.next;
            len++;
        }
        
        k = k % len;
        
        for(int i = 0; i < k; i++) {
            fast = fast.next;
        }
        while(fast.next != null) {
            fast = fast.next;
            slow = slow.next;
        }
        fast.next = head;
        fakeHead.next = slow.next;
        slow.next = null;
        
        return fakeHead.next;
    }
}