%% @author rolong@vip.qq.com
%% 本代码来自 瑞仙的Erlang开发博客
%% http://blog.csdn.net/zhongruixian
-module(astar1).
-export([
find_path/2
,test/2
]).
-record(state, {
open_trees %% 开启列表
,close_sets %% 关闭列表
,parents_trees %% 父节点列表
,xy %% 目标点
}).
-record(point, {
xy = {0, 0}
,g = 0
,h = 0
,f = 0
}).
%% 1为向上，按顺时针依次为1~8
-define(DIRS, [1,2,3,4,5,6,7,8]).
%%' API
test(XY1, XY2) ->
Path = find_path(XY1, XY2),
io:format("Path:~n~p~n", [Path]),
show_path(Path).
find_path(XY1, XY2) ->
State = #state{
open_trees = gb_trees:empty()
,close_sets = gb_sets:new()
,xy = XY2
,parents_trees = gb_trees:empty()
},
StartPoint = #point{xy = XY1},
OpenTrees = gb_trees:enter(XY1, {0, 0, 0}, State#state.open_trees),
State1 = State#state{open_trees = OpenTrees},
find_next_point(StartPoint, State1).
%%.
%%' priv
-spec walkable({X, Y}) -> true | false when
X :: integer(),
Y :: integer().
%%'walkable函数根据具体点阵实现
%% 示例如下：
walkable({X, Y}) ->
{Row, Col} = map(size),
case X >= 0 andalso Y >= 0 andalso X < Row andalso Y < Col of
true ->
Block = map(block),
Nth = X + Y * Row + 1,
case string:substr(Block, Nth, 1) of
"1" -> true;
"0" -> false
end;
false -> false
end;
walkable(_) -> false.
map(size) ->
{20, 10};
map(block) ->
%01234567890123456789
"11111111111111111111" % 0
"11111111111111111111" % 1
"11111111111111111111" % 2
"11111111000111111111" % 3
"11111111000111111111" % 4
"11111111000111111111" % 5
"11111111000111111111" % 6
"11111111000111111111" % 7
"11111111000111111111" % 8
"11111111111111111111" % 9
.
%%.
find_next_point(#point{xy = XY}, #state{xy = XY} = State) ->
get_path(XY, State#state.parents_trees, [XY]);
find_next_point(#point{xy = XY} = CurPoint, State) ->
State1 = open2close(CurPoint, State),
%% 将周围点添加到开放列表中
AroundPoints = find_around_points(CurPoint, State1),
State2 = add_open_trees(AroundPoints, XY, State1),
case find_min_f_point(State2) of
none ->
io:format("Error coord:~w~n", [CurPoint#point.xy]),
[];
NextPoint ->
find_next_point(NextPoint, State2)
end.
find_min_f_point(State) ->
Iter = gb_trees:iterator(State#state.open_trees),
find_min_f_point(Iter, -1, none).
find_min_f_point(Iter, F, Point) ->
case gb_trees:next(Iter) of
none -> Point;
{XY, {G1, H1, F1}, Iter1} ->
case F1 < F orelse F =:= -1 of
true ->
Point1 = #point{
xy = XY
,g = G1
,h = H1
,f = F1
},
find_min_f_point(Iter1, F1, Point1);
false ->
find_min_f_point(Iter1, F, Point)
end
end.
xy2point({CurX, CurY}, ParentPoint, {DstX, DstY}) ->
#point{
xy = {X, Y}
,g = G
} = ParentPoint,
AddG = if
CurX =:= X -> 10;
CurY =:= Y -> 10;
true -> 14
end,
CurH = (erlang:abs(CurX - DstX) + erlang:abs(CurY - DstY)) * 10,
CurG = G + AddG,
#point{
xy = {CurX, CurY}
,g = CurG
,h = CurH
,f = CurG + CurH
}.
%% 找出周围点
find_around_points(Point, State) ->
#state{
close_sets = CloseSets
} = State,
#point{
xy = {X, Y}
} = Point,
F = fun(Dir, Acc) ->
XY1 = get_next_coord(Dir, X, Y),
case walkable(XY1) of
true ->
case gb_sets:is_element(XY1, CloseSets) of
true -> Acc;
false ->
Point1 = xy2point(XY1, Point, State#state.xy),
[Point1 | Acc]
end;
false -> Acc
end
end,
lists:foldl(F, [], ?DIRS).
add_open_trees([Point | Tail], ParentXY, State) ->
case gb_trees:lookup(Point#point.xy, State#state.open_trees) of
{_XY, {G, _H, _F}} ->
case Point#point.g < G of
true ->
State1 = add_open_trees1(Point, ParentXY, State),
add_open_trees(Tail, ParentXY, State1);
false ->
add_open_trees(Tail, ParentXY, State)
end;
none ->
State1 = add_open_trees1(Point, ParentXY, State),
add_open_trees(Tail, ParentXY, State1)
end;
add_open_trees([], _ParentXY, State) ->
State.
add_open_trees1(Point, ParentXY, State) ->
#point{xy = XY, g = G, h = H, f = F} = Point,
OpenTrees1 = gb_trees:enter(XY, {G, H, F}, State#state.open_trees),
ParentsTrees1 = gb_trees:enter(XY, ParentXY, State#state.parents_trees),
State#state{
open_trees = OpenTrees1
,parents_trees = ParentsTrees1
}.
open2close(Point, State) ->
OpenTrees = gb_trees:delete(Point#point.xy, State#state.open_trees),
CloseSets = gb_sets:add(Point#point.xy, State#state.close_sets),
State#state{
open_trees = OpenTrees
,close_sets = CloseSets
}.
get_next_coord(1,X,Y)->
{X,Y-1};
get_next_coord(2,X,Y)->
{X+1,Y-1};
get_next_coord(3,X,Y)->
{X+1,Y};
get_next_coord(4,X,Y)->
{X+1,Y+1};
get_next_coord(5,X,Y)->
{X,Y+1};
get_next_coord(6,X,Y)->
{X-1,Y+1};
get_next_coord(7,X,Y)->
{X-1,Y};
get_next_coord(8,X,Y)->
{X-1,Y-1}.
get_path(XY, ParentsTrees, Acc) ->
case gb_trees:lookup(XY, ParentsTrees) of
none -> Acc;
{value, XY1} ->
get_path(XY1, ParentsTrees, [XY1 | Acc])
end.
%%'用于测试打印
show_path(XYs) ->
Block = map(block),
{Row, Col} = map(size),
Len = Row * Col,
show_path(XYs, Row, Col, Len, Block).
show_path([{X, Y} | XYs], Row, Col, Len, Block) ->
LeftLen = X + Y * Row,
RightLen = Len - LeftLen - 1,
Left = string:left(Block, LeftLen),
Right = string:right(Block, RightLen),
Block1 = Left ++ "*" ++ Right,
show_path(XYs, Row, Col, Len, Block1);
show_path([], Row, _Col, Len, Block) ->
show_path1(Row, Len, Block, "").
show_path1(_Row, Len, _Block, Acc) when Len =< 0 ->
io:format("~n~s~n", [Acc]);
show_path1(Row, Len, Block, Acc) ->
Len1 = Len - Row,
Left = string:left(Block, Row),
Block1 = string:right(Block, Len1),
Acc1 = Acc ++ Left ++ "\n",
show_path1(Row, Len1, Block1, Acc1).
%%.
%%.
%%% vim: set foldmethod=marker filetype=erlang foldmarker=%%',%%.:
原文地址：http://blog.csdn.net/zhongruixian/article/details/45244501
