gb_trees:take_largest/1

从树里提取最大的元素

用法：

take_largest(Tree1) -> {Key, Val, Tree2}

内部实现：

-spec take_largest(Tree1) -> {Key, Val, Tree2} when
      Tree1 :: gb_tree(),
      Tree2 :: gb_tree(),
      Key :: term(),
      Val :: term().

take_largest({Size, Tree}) when is_integer(Size), Size >= 0 ->
    {Key, Value, Smaller} = take_largest1(Tree),
    {Key, Value, {Size - 1, Smaller}}.

take_largest1({Key, Value, Smaller, nil}) ->
    {Key, Value, Smaller};
take_largest1({Key, Value, Smaller, Larger}) ->
    {Key1, Value1, Larger1} = take_largest1(Larger),
    {Key1, Value1, {Key, Value, Smaller, Larger1}}.

返回一个 {Key, Val, Tree2} 的元组，Key 是树 Tree1 里最大的键，Val 是跟键 Key 相关联的值，Tree2 是删去该键相应节点后的树（这里假设该树不是一个空树）。

Orddict = orddict:from_list([{pear, 7}, {orange, 5}, {apple, 2}]),
Tree = gb_trees:from_orddict(Orddict),
gb_trees:take_largest(Tree).