CareerCup

Have two pointers. Start one from the head and start the second from nth node. Increment each one at a time. By the time the second pointer hits the last node, the first node will be pointing to the nth node from the last.

private static Node find（Node root，int n）{
Node ahead = root；
Node behind = root；
for（int i=0；i＜n；i++）{
ahead=ahead.next；
if（ahead==null）
return null；
}
while（ahead.next!=null）{
ahead =ahead.next；
behind=behind.next；
}
return behind；
}