[练习]erlang算法练习--dijstra

dijistra是一种贪心算法 用来求无向图两点间的最短距离

具体的内容我不多说了..

这边写的代码没有经过太多的验证 用了一个简单的例子做 所以也许还会有些地方有些问题

用的例子是

blog.csdn.net/v_july_v/article/details/6096981

内的 

图和具体步骤如下:

 

 

具体代码如下:

%% @author cc fairjm
%% @doc @todo Add description to dijstra_run.


-module(dijstra_run).

%% ====================================================================
%% API functions
%% ====================================================================
-export([run/0]).

run() ->
  %%定义距离的格式 这边的定义为 List中放入Tuple的结构(这样可以方便后面用lists库内的key系列函数)
  %%Tuple的结构定义为 {节点,[{与节点相连的其他节点,距离}....]}
  Distance=[{a,[{b,6},{c,3}]},
			{b,[{a,6},{c,2},{d,5}]},
			{c,[{a,3},{b,2},{d,3},{e,4}]},
			{d,[{e,2},{b,5},{c,3},{f,3}]},
			{e,[{c,4},{d,2},{f,5}]},
			{f,[{d,3},{e,5}]}
  ],
  %%初始状态
  Init=[b,c,d,e,f],
  %%终状态
  Final=[a],
  %%路线初始化  结构依旧为List中放入Tuple Tuple的含义为{目标节点,目标节点和A的距离,路线}
  Route=[{a,0,[a]},{b,infinity,[a]},{c,infinity,[a]},{d,infinity,[a]},{e,infinity,[a]},{f,infinity,[a]}],
  calcu(Init,Final,Route,Distance)
.


%% ====================================================================
%% Internal functions
%% ====================================================================
calcu([],_Final,Route,_Distance)->
 Route	
;

calcu(Init,Final,Route,Distance) ->
	MinLists=lists:foldl(fun(Elem,In)->
				  %%当前元素到初始节点A的距离
				  {Elem,Elem_to_A,Elem_to_A_List}=lists:keyfind(Elem, 1,Route),
				  %%遍历当前元素和各个节点的距离
				  {Elem,List}=lists:keyfind(Elem, 1, Distance),		
				  %%过滤如果目标节点比在当前表里的还大那就没必要继续算下去了
				  Shorter_List=lists:filter(fun({Elem2,Dis})->
									%%目标节点的真实距离=当前元素到初始节点A的距离+当前元素到A的距离
									Dis_to_A=Dis+Elem_to_A,   
									{Elem2,Elem2_to_A,_}=lists:keyfind(Elem2, 1,Route),
									Elem2_to_A > Dis_to_A
								end	, List),
				  In++lists:map(fun({Elem2,Dis}) -> {Elem2,Dis+Elem_to_A,Elem_to_A_List++[Elem2]} end, Shorter_List)		
				end, [], Final),	
	Tuple=lists:nth(1, lists:keysort(2,MinLists)),
	%%拿出End用来后面更新Route的内容
	{End,_,_}=Tuple,
	NewRoute=lists:keyreplace(End, 1, Route, Tuple),
	NewFinal=Final++[End],
	NewInit=Init--[End],
	io:format("~p~n", [NewRoute]),
	calcu(NewInit,NewFinal,NewRoute,Distance)
.

 代码运行如下:

28> c("dijstra_run").
{ok,dijstra_run}
29> dijstra_run:run().
[{a,0,[a]},
{b,infinity,[a]},
{c,3,[a,c]},
{d,infinity,[a]},
{e,infinity,[a]},
{f,infinity,[a]}]
[{a,0,[a]},
{b,5,[a,c,b]},
{c,3,[a,c]},
{d,infinity,[a]},
{e,infinity,[a]},
{f,infinity,[a]}]
[{a,0,[a]},
{b,5,[a,c,b]},
{c,3,[a,c]},
{d,6,[a,c,d]},
{e,infinity,[a]},
{f,infinity,[a]}]
[{a,0,[a]},
{b,5,[a,c,b]},
{c,3,[a,c]},
{d,6,[a,c,d]},
{e,7,[a,c,e]},
{f,infinity,[a]}]
[{a,0,[a]},
{b,5,[a,c,b]},
{c,3,[a,c]},
{d,6,[a,c,d]},
{e,7,[a,c,e]},
{f,9,[a,c,d,f]}]
[{a,0,[a]},
{b,5,[a,c,b]},
{c,3,[a,c]},
{d,6,[a,c,d]},
{e,7,[a,c,e]},
{f,9,[a,c,d,f]}]