原题链接: https://oj.leetcode.com/problems/remove-nth-node-from-end-of-list/

public ListNode removeNthFromEnd(ListNode head, int n) {
    if (head == null) return null;
    if (n == 0) return head;

    ListNode cursor = head;
    int size = 0;

    while (cursor != null) {
        cursor = cursor.next;
        size++;
    }

    cursor = head;
    int targetIndex = size - n;
    int cursorIndex = 0;
    ListNode prevNode = null;

    while (cursorIndex < targetIndex) {
        prevNode = cursor;
        cursor = cursor.next;
        cursorIndex++;
    }

    if (prevNode == null) {
        head = cursor.next;
    } else {
        prevNode.next = cursor.next;
    }

    return head;
}