19. Remove Nth Node From End of List

题目

Given a linked list, remove the nth node from the end of list and return its head.For example,   Given linked list: 1->2->3->4->5, and n = 2.   After removing the second node from the end, the linked list becomes 1->2->3->5.Note:Given n will always be valid.Try to do this in one pass.

解析

• 两种思路
• 思路一：第一遍遍历得到链表的长度，第二遍走cnt-n步，注意边界条件
• 思路二：两个指针，第一个先走n-1步，然后两个指针一起走

// 19. Remove Nth Node From End of Listclass Solution {public:    ListNode* removeNthFromEnd(ListNode* head, int n) {        ListNode* cur = head;        if (head==NULL)        {            return NULL;        }        int cnt = 0;        while (cur!=NULL)        {            cnt++;            cur = cur->next;        }        cur = head;        int pos = cnt - n+1;        if (pos==1)        {            return cur->next;        }        pos = pos - 2;        while (pos)        {            cur = cur->next;            pos--;        }        ListNode* dete = cur->next;        if (dete->next)        {            cur->next = cur->next->next;        }        else        {            cur->next = NULL;        }                        //delete dete;        return head;    }};

题目来源