C++进阶练习删除链表的倒数第N个结点详解

class Solution {
public:
    int getLength(ListNode* head) {
        int length = 0;
        while (head) {
            ++length;
            head = head->next;
        }
        return length;
    }
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode* dummy = new ListNode(0, head);
        int length = getLength(head);
        ListNode* cur = dummy;
        for (int i = 1; i < length - n + 1; ++i) {
            cur = cur->next;
        }
        cur->next = cur->next->next;
        ListNode* ans = dummy->next;
        delete dummy;
        return ans;
    }
};

class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
     ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;

        ListNode* p = dummyHead;
        ListNode* q = dummyHead;
        for( int i = 0 ; i < n + 1 ; i ++ ){
            q = q->next;
        }
        while(q){
            p = p->next;
            q = q->next;
        }
        ListNode* delNode = p->next;
        p->next = delNode->next;
        delete delNode;
        ListNode* retNode = dummyHead->next;
        delete dummyHead;
        return retNode;
    }
};