Q22_RemoveLastKNode.java

package jianzhi_offer;

/**
 * @author weiyuwang
 * @since 2019/1/29 10:13
 */
public class Q22_RemoveLastKNode {
    public class ListNode {
        int val;
        ListNode next;

        ListNode(int x) {
            val = x;
        }
    }

    /**
     * LeetCode 19
     * 给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。
     *
     * 剑指offer中只是定位那个倒数第 K 个结点。
     * @param head
     * @param n
     * @return
     */
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if (head == null) {
            return null;
        }
        ListNode fast = head;
        // slow 设计为目标结点的前一个结点
        ListNode slow = head;
        for (int i = 0; i < n; i++) {
            fast = fast.next;
        }

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

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

        slow.next = slow.next.next;

        return head;
    }
}