Find Nth to the last element in the list.

FindNth.java

/**
 * Problem: Find the nth to the end of the linked list.
 */

public class FindNth {
    /**
     * Solution:
     * A simple math - nth to the end equals to: the length - n
     * from the beginning.
     * We can first calculate the length of the linked list then print
     * the (length - n) node from the beginning.
     *
     * Analysis:
     * Time Complexity: O(N), where N means the length of the list.
     * Space Complexity: O(1)
     */
    public static int getNth(ListNode head, int n) {
        if (head == null || n < 0) return -1;

        /* Calculate the length of the linked list */
        int length = 0;
        ListNode current = head;
        while (current != null) {
            current = current.next;
            length++;
        }

        int nth = length - n;
        current = head;
        while (nth != 0) {
            current = current.next;
            nth--;
        }

        return current.value;
    }
}