Leetcode 19. Remove Nth Node From End of List
文章作者：Tyan
博客：noahsnail.com | CSDN | 簡書
1. Description
2. Solution
- Version 1
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
if(!head || !head->next) {
return nullptr;
}
int number = 0;
ListNode* current = head;
while(current) {
if(current->next) {
number += 2;
current = current->next->next;
}
else {
number += 1;
current = current->next;
}
}
int target = number - n;
if(target == 0) {
return head->next;
}
ListNode* pre = head;
current = head->next;
int count = 1;
while(count != target) {
pre = current;
current = current->next;
count++;
}
pre->next = pre->next->next;
return head;
}
};
- Version 2
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
if(!head || !head->next) {
return nullptr;
}
int number = 0;
int count = 0;
ListNode* middle = head;
ListNode* current = head;
while(current) {
count++;
middle = middle->next;
if(current->next) {
number += 2;
current = current->next->next;
}
else {
number += 1;
current = current->next;
}
}
int target = number - n;
if(target == 0) {
return head->next;
}
ListNode* pre = nullptr;
int index = 0;
if(target > count) {
index = count;
current = middle;
}
else {
current = head;
}
while(index != target) {
pre = current;
current = current->next;
index++;
}
pre->next = pre->next->next;
return head;
}
};
- Version 3
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
ListNode* new_head = new ListNode(0);
new_head->next = head;
ListNode* current = new_head;
for(int i = 0; i < n + 1; i++) {
current = current->next;
}
ListNode* pre = new_head;
while(current) {
current = current->next;
pre = pre->next;
}
pre->next = pre->next->next;
return new_head->next;
}
};