建立一个双向循环链表,并在里面增加一个freq,初使为0,每当lcate(l,x)访问X一次相的freq加1,同时链表顺序也按freq的大小非递增排列-A two-way circular linked list, and in which an additional freq, initialization is 0, when lcate (l, x) access to a phase freq X plus 1, but also by freq list the size of the