【19】Remove Nth Node From End of List

Given a linked list, remove the n^th 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.

链表基础题，让一前一后两个指针间隔出n的距离，那么先走的指针走到最后一个节点时，后走的指针就在倒数第n个节点。因为有可能删掉第一个节点，所以加一个头节点编码会方便一点

ListNode* removeNthFromEnd(ListNode* head, int n) { if(!head)return NULL; ListNode* pHead=new ListNode(0); pHead->next=head; ListNode* l1=pHead; ListNode* l2=pHead; while(n--)l2=l2->next; while(l2->next){ l1=l1->next; l2=l2->next; } l1->next=l1->next->next; return pHead->next; }