JZ15 反转链表

func ReverseList( head *ListNode ) *ListNode {
    // write code here
    if head == nil || head.Next == nil {
        return head
    }

    var pre, cur, post *ListNode = nil, head, head.Next
    for cur != nil {
        post = cur.Next
        cur.Next = pre
        pre = cur
        cur = post 
    }
    return pre
}