Leetcode-19. Remove Nth Node From End of List

题目

思路

代码

class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
if(NULL==head || n<1) return head;
ListNode* p = head;
while(p) {
n--;
p = p->next;
}
if(n == 0)
return head->next;
if(n < 0) {
p = head;
while(++n)
p = p->next;
p->next = p->next->next;
}
return head;
}
};

class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
if(NULL==head || n<1) return head;
ListNode *h = new ListNode(0);
h->next = head;
ListNode* p1 = h, *p2 = h;
for(int i=0; i<n && p1; i++, p1 = p1->next);
if(NULL == p1)
return head;
while(p1->next) {
p1 = p1->next;
p2 = p2->next;
}
p2->next = p2->next->next;
return h->next;
}
};