19. Remove Nth Node From End of List

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?

TowPointers

public ListNode removeNthFromEnd(ListNode head, int n) {
    ListNode fast = head, slow = null;
    for(int i = 0; i <= n; i++) {
        if(fast == null) return head.next;
        fast = fast.next;
    }
    slow = head;
    while(fast != null) {
        fast = fast.next;
        slow = slow.next;
    }
    slow.next = slow.next.next;
    return head;
}

Recursive ```java

public ListNode removeNthFromEndRecursive(ListNode head, int n) { ListNode sentinel = new ListNode(0); sentinel.next = head; dfs(sentinel, n); return sentinel.next; }

public Result dfs(ListNode head, int target) { if(head == null) return new Result(null, 0); Result result = dfs(head.next, target); if(result.cnt == target) { head.next = result.n.next; result.n.next = null; } result.n = head; result.cnt++; return result; }

class Result { ListNode n; int cnt; public Result(ListNode n, int cnt) { this.n = n; this.cnt = cnt; } } ```