Talk is cheap.

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func findKthToTail(pHead *ListNode, k int) *ListNode {
    if pHead == nil || k <= 0 {
        return nil
    }
    pre := pHead
    post := pre
    for ; k > 0; k-- {
        if pre != nil {
            pre = pre.Next
        } else {
            return nil
        }
    }
    for pre != nil {
        pre = pre.Next
        post = post.Next
    }
    return post
}