19. 删除链表的倒数第N个节点
1、题目介绍
给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。
试题链接：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/
2、java
2.1、遍历两次
public static ListNode removeNthFromEnd(ListNode head, int n) {
if(head == null || head.next == null) return null;
//求链表长度
ListNode p = head;
int size = 0;
while (p != null) {
size++;
p = p.next;
}
if(n == size) return head.next;
p = head;
for(int i = 2;i <= size - n;i++ ) {
p = p.next;
}
p.next = p.next.next;
return head;
}
测试结果：
2.1、遍历一次
public static ListNode removeNthFromEnd(ListNode head, int n) {
if(head == null || head.next == null) return null;
//求链表长度
ListNode p = head;
int flag = 0;
while (p != null && p.next != null) {
ListNode temp = p.next;
for(int i = 0;i < n;i++) {
if(temp == null) {
flag = 1;
break;
}
temp = temp.next;
}
if(flag == 1) {
return head.next;
}
if(temp != null) {
p = p.next;
}else {
p.next = p.next.next;
return head;
}
}
return head;
}
测试结果：
3、C语言
3.1、遍历两次
struct ListNode* removeNthFromEnd(struct ListNode* head, int n){
if(head == NULL || head->next == NULL) return NULL;
//求链表长度
struct ListNode* p = head;
int size = 0;
while (p != NULL) {
size++;
p = p->next;
}
if(n == size) return head->next;
p = head;
for(int i = 2;i <= size - n;i++ ) {
p = p->next;
}
p->next = p->next->next;
return head;
}
测试结果：
3.1、遍历一次
struct ListNode* removeNthFromEnd(struct ListNode* head, int n){
if(head == NULL || head->next == NULL) return NULL;
//求链表长度
struct ListNode* p = head;
int flag = 0;
while (p != NULL && p->next != NULL) {
struct ListNode* temp = p->next;
for(int i = 0;i < n;i++) {
if(temp == NULL) {
flag = 1;
break;
}
temp = temp->next;
}
if(flag == 1) {
return head->next;
}
if(temp != NULL) {
p = p->next;
}else {
p->next = p->next->next;
return head;
}
}
return head;
}
测试结果：
