LeetCode-19. Remove Nth Node From End of ListLevel up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.https://leetcode.com/problems/remove-nth-node-from-end-of-list/

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Example 1:

Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]

Example 2:

Input: head = [1], n = 1
Output: []

Example 3:

Input: head = [1,2], n = 1
Output: [1]

Constraints:

• The number of nodes in the list is sz.
• 1 <= sz <= 30
• 0 <= Node.val <= 100
• 1 <= n <= sz

Follow up: Could you do this in one pass?

 

【C++】

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode *forwoard = head, *backwoard = head;
        int i = 0;
        while (forwoard) {
            forwoard = forwoard->next;
            if (i++ > n) {backwoard = backwoard->next;}
        }
        if (i < n) {return head;}
        else if (i == n) {return head->next;}
        else {
            backwoard->next = backwoard->next
                ? backwoard->next->next : nullptr;
        }
        return head;
    }
};

【Java】

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode forwoard = head, backwoard = head;
        int i = 0;
        while (forwoard != null) {
            if (i++ > n) {backwoard = backwoard.next;}
            forwoard = forwoard.next;
        }
        if (i < n) {return head;}
        else if (i == n) {return head.next;}
        else {
            backwoard.next = backwoard.next != null
                ? backwoard.next.next : null;
        }
        return head;
    }
}