Talk is cheap.

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func entryNodeOfLoop(head *ListNode)  *ListNode{
    pre := head
    post := head
    for pre != nil && pre.Next != nil {
        pre = pre.Next.Next
        post = post.Next
        if pre == post {
            pre = head
            for pre != post {
                pre = pre.Next
                post = post.Next
            }
            return pre
        }
    }
    return nil
}