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 List
class 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