44--remove-nth-node-from-end-of-list.java

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode newHead = new ListNode(-1);
        newHead.next = head;
        dfs(newHead, n + 1);
        return newHead.next;
    }
    public int dfs(ListNode node, int k) {
        if (node == null) return 0;
        int index = 1 + dfs(node.next, k);
        if (index == k) {
            node.next = node.next.next;
        }
        return index;
    }
} // TC: O(n), SC: O(n)

// -1->1->2->3->4->5->null