题解 | #调整牛群顺序#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* moveNthToEnd(ListNode* head, int n) {
        // write code here
        if(!head)
        {
            return NULL;
        }
        if(n <=1)
        {
            return head;

        }
        struct ListNode * p = head;
        int count = 0;
        while(p->next)
        {
            p = p->next;
            count++;
        }
        struct ListNode * m = head;
        struct ListNode * q = head;
        if(count+1 == n)
        {
            p->next = head;
            head = head->next;
            p->next->next = nullptr;

        }
        for(int i = 0;i <= count - n;i++)
        {
            q = m;
            m = m->next;

        }
        q->next = m->next;
        m->next = nullptr;
        p->next = m;
        return head;
        

    }
};