leetcode19 Remove Nth Node From End of List(删除链表的倒数第N个节点)

版权声明：个人博客网址 https://29dch.github.io/ GitHub网址 https://github.com/29DCH，欢迎大家前来交流探讨和fork! https://blog.csdn.net/CowBoySoBusy/article/details/83510119

题目链接
https://leetcode.com/problems/remove-nth-node-from-end-of-list/
知识点：
考察链表、指针相关知识

思路：
1.先遍历一遍计算得到链表的长度,再遍历一遍删除倒数第n个节点
2.双指针法:p指针开始的时候指向虚拟头结点,p、q指针之间的距离一直保持为n,p
、q指针同时往链表尾移动直到q指针指向NULL,代表此时p指针指向的元素就是待删除的元素的前一个元素,再把后面那个元素删除即可.这种方法只遍历一次链表就解决问题了.

下面代码采用思路2的思路.
AC代码：

class Solution
{
public:
ListNode* removeNthFromEnd(ListNode* head, int n)
{
assert(n>=0);
ListNode* dummyhead = new ListNode(0);
dummyhead->next = head;
ListNode* p=dummyhead;
ListNode* q=dummyhead;
for(int i=0; i<n+1; i++)
{
assert(q);
q=q->next;
}
while(q!=NULL)
{
p=p->next;
q=q->next;
}
ListNode* delNode = p->next;
p->next=delNode->next;
delete delNode;
ListNode* retNode = dummyhead->next;
delete dummyhead;
return retNode;
}
};

AC代码加测试如下:

#include <bits/stdc++.h>
using namespace std;

struct ListNode
{
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};

ListNode* createLinkedList(int arr[], int n)
{
if(n == 0)
return NULL;
ListNode* head = new ListNode(arr[0]);
ListNode* curNode = head;
for(int i=1; i<n; i++)
{
curNode->next = new ListNode(arr[i]);
curNode = curNode->next;
}
return head;
}

void printLinkedList(ListNode* head)
{
ListNode* curNode = head;
while(curNode!=NULL)
{
cout<<curNode->val<<" -> ";
curNode = curNode->next;
}
cout<<"NULL"<<endl;
}

void deleteLinkedList(ListNode* head)
{
ListNode* curNode = head;
while(curNode!=NULL)
{
ListNode* delNode = curNode;
curNode = curNode->next;
delete delNode;
}
}

class Solution
{
public:
ListNode* removeNthFromEnd(ListNode* head, int n)
{
assert(n>=0);
ListNode* dummyhead = new ListNode(0);
dummyhead->next = head;
ListNode* p=dummyhead;
ListNode* q=dummyhead;
for(int i=0; i<n+1; i++)
{
assert(q);
q=q->next;
}
while(q!=NULL)
{
p=p->next;
q=q->next;
}
ListNode* delNode = p->next;
p->next=delNode->next;
delete delNode;
ListNode* retNode = dummyhead->next;
delete dummyhead;
return retNode;
}
};
int main()
{
int arr[]= {1,2,3,4,5};
int n = sizeof(arr)/sizeof(int);
ListNode* head = createLinkedList(arr,n);
printLinkedList(head);
ListNode* head1 = Solution().removeNthFromEnd(head,2);
printLinkedList(head1);
deleteLinkedList(head1);
return 0;
}

阅读更多