Given a linked list, remove the nth node from the end of list and return its head.
For 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.
Try to do this in one pass.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* removeNthFromEnd(struct ListNode* head, int n) 
{
    struct ListNode* fast = head;
    struct ListNode* slow = head;

    while (fast != NULL) 
    {
        fast = fast->next;
        if (n-- < 0) 
            slow = slow->next;
    }
    
    if (n == 0) 
    {
        /*free head if necessary*/
        head = head->next;
    }
        
    else 
    {
        /*free slow->next if necessary*/
        slow->next = slow->next->next;
    }
        
    return head;
}

2021.06.20更新

/**
 * 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* dummy = new ListNode(-1,head);
        ListNode* fast = head,*slow = dummy;
        for(int i = 0;i < n;i++)
        {
            if(fast)
                fast = fast->next;    
        }

        while(fast)
        {
            fast = fast->next;
            slow = slow->next;
        }

        slow->next = slow->next->next;
        return dummy->next;
    }
};

执行效率:

执行用时：0 ms, 在所有 C++ 提交中击败了100.00%的用户
内存消耗：10.4 MB, 在所有 C++ 提交中击败了26.30%的用户

进一步优化代码:

/**
 * 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* dummy = new ListNode(-1,head);
        ListNode* fast = head,*slow = dummy;

        while(fast)
        {
            fast = fast->next;
            if(--n < 0)
                slow = slow->next;
        }

        slow->next = slow->next->next;
        return dummy->next;
    }
};

class Solution {
public:
    int divide(int dividend, int divisor) {
        if (dividend == INT_MIN && divisor == -1) {
            return INT_MAX;
        }
        long dvd = labs(dividend), dvs = labs(divisor), ans = 0;
        int sign = dividend > 0 ^ divisor > 0 ? -1 : 1;
        while (dvd >= dvs) {
            long temp = dvs, m = 1;
            while (temp << 1 <= dvd) {
                temp <<= 1;
                m <<= 1;
            }
            dvd -= temp;
            ans += m;
        }
        return sign * ans;
    }
};