19. Remove Nth Node From End of List

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题目

https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/

想法

比较简单，就是记录着扫着的ptr之前n位的地址就可以了。

答案

一次AC

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode* target = head;
        ListNode* ptr = head;
        for (int i = 0; i < n; i++) {
            ptr = ptr->next;
        }
        if (ptr == NULL) {
            ListNode* tmp = head;
            head = head->next;
            free(tmp);
            return head;
        }
        while(ptr->next != NULL) {
            ptr = ptr->next;
            target = target->next;
        }
        ListNode* tmp = target->next;
        target->next = tmp->next;
        free(tmp);
        return head;
    }
};