19. Remove Nth Node From End of List

• Difficulty: Medium

• Topics: Linked List, Two Pointers

• Similar Questions:

Problem:

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

Example:

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:

Given n will always be valid.

Follow up:

Could you do this in one pass?

Solutions:

/**
 * 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* front = head;
        for (int i = 0; i < n; ++i) {
            if (front == NULL)  return NULL;
            front = front->next;
        }

        if (front == NULL) {
            return head->next;
        }

        front = front->next;

        ListNode* cur = head;
        while (front != NULL) {
            front = front->next;
            cur = cur->next;
        }

        cur->next = cur->next->next;
        return head;

    }
};