erlang 二叉树

-module(ltree).

-export([is_leaf/1,sum/1,max/1,is_ordered/1,insert/2]).
-export([test/0]).

-record(btree, {value, ltree=nil, rtree=nil}).

% 判断某个节点是否为叶子节点
is_leaf(#btree{ltree=nil,rtree=nil}) ->
    true;
is_leaf(#btree{}) ->
    false.

% 整棵树所有节点的值的和
sum(#btree{value=Value, ltree=nil, rtree=nil}) ->
    Value;
sum(#btree{value=Value, ltree=nil, rtree=Rtree}) ->
    sum(Rtree) + Value;
sum(#btree{value=Value, ltree=Ltree, rtree=nil}) ->
    sum(Ltree) + Value;
sum(#btree{value=Value, ltree=Ltree, rtree=Rtree}) ->
    sum(Ltree) + sum(Rtree) + Value.

% 整棵树节点值的最大值
max(#btree{value=Value, ltree=nil, rtree=nil}) ->
    Value;
max(#btree{value=Value, ltree=nil, rtree=Rtree}) ->
    erlang:max(Value, max(Rtree));
max(#btree{value=Value, ltree=Ltree, rtree=nil}) ->
    erlang:max(Value, max(Ltree));
max(#btree{value=Value, ltree=Ltree, rtree=Rtree}) ->
    erlang:max(Value, erlang:max(max(Ltree), max(Rtree))).

% 判断一个二叉树是否有序的
is_ordered(#btree{ltree=nil, rtree=nil}) ->
    true;
is_ordered(#btree{value=Value, ltree=Ltree, rtree=nil}) ->
    if 
	Value >= Ltree#btree.value ->
	    is_ordered(Ltree);
	true -> false
    end;
is_ordered(#btree{value=Value, ltree=nil, rtree=Rtree}) ->
    if 
	Value =< Rtree#btree.value ->
	    is_ordered(Rtree);
	true -> false
    end;
is_ordered(#btree{value=Value, ltree=Ltree, rtree=Rtree}) ->
    if 
	Value >= Ltree#btree.value, Value =< Rtree#btree.value ->
	    is_ordered(Ltree),
	    is_ordered(Rtree);
	true -> false
    end.

% 如果一个二叉树是有序的，往该树再插节点，保持树有序
insert(NewValue, #btree{value=Value, ltree=nil, rtree=nil}) ->
    if 
	Value > NewValue ->
	    #btree{value=Value, 
		   ltree=#btree{value=NewValue}, 
		   rtree=nil};
	true ->
	    #btree{value=Value, 
		   ltree=nil, 
		   rtree=#btree{value=NewValue}}
    end;
insert(NewValue, #btree{value=Value, ltree=Ltree, rtree=nil}) ->
    if
	Value =< NewValue ->
	    #btree{value=Value, 
		   ltree=Ltree, 
		   rtree=#btree{value=NewValue}};
	true ->
	    #btree{value=Value, 
		   ltree=insert(NewValue, Ltree), 
		   rtree=nil}
    end;
insert(NewValue, #btree{value=Value, ltree=nil, rtree=Rtree}) ->
    if
	Value > NewValue ->
	    #btree{value=Value, 
		   ltree=#btree{value=NewValue}, 
		   rtree=Rtree};
	true ->
	    #btree{value=Value, 
		   ltree=nil, 
		   rtree=insert(NewValue, Rtree)}
    end;
insert(NewValue, #btree{value=Value, ltree=Ltree, rtree=Rtree}) ->
    if 
	Value > NewValue ->
	    #btree{value=Value, 
		   ltree=insert(NewValue, Ltree), 
		   rtree=Rtree};
	true ->
	    #btree{value=Value, 
		   ltree=Ltree, 
		   rtree=insert(NewValue, Rtree)}
    end.



test()->

Btree1 = #btree{value=1},
    Btree2 = #btree{value=4, 
		    ltree=#btree{value=3}, 
		    rtree=#btree{value=5}},
    Btree3 = #btree{value=3, % Btree3是有序的
		    ltree=#btree{value=2}, 
		    rtree=Btree2},
    Btree4 = #btree{value=1, 
		    ltree=#btree{value=2}, 
		    rtree=#btree{value=3}},
    Btree5 = insert(1, Btree3), % Btree5也是有序的

    Btrees = [Btree1, Btree2, Btree3, Btree4, Btree5],


    TestPrint = 
    	fun(#btree{}=Btree) ->
    		io:format("~p~n Sum: ~.3p Max: ~.3p, IsLeaf?: ~.3p, IsOrdered?: ~.3p~n", 
    			  [Btree, sum(Btree), max(Btree), is_leaf(Btree), is_ordered(Btree)])
    	end,

    lists:foreach(TestPrint, Btrees).

祝你好运！！！