0019.remove_nth_node_from_end_of_list_M.c

/**
 * https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/
 * 2015/07
 * 0 ms
 */

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode * removeNthFromEnd(struct ListNode * head, int n)
{
    if(n <= 0 || head == NULL)
        return head;
    
    struct ListNode * p1;
    struct ListNode * p2;
    for(p2 = head; n > 0; n --)
        p2 = p2 -> next;
    if(p2 == NULL)
    {
        p1 = head -> next;
        free(head);
        return p1;
    }
    p1 = head;
    p2 = p2 -> next;
    
    while(p2 != NULL)
    {
        p1 = p1 -> next;
        p2 = p2 -> next;
    }
    p2 = p1 -> next;
    p1 -> next = p2 -> next;
    free(p2);
    return head;
}