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algorithm-php/src/Query/DijkstraQuery.php at master · m9rco/algorithm-php · GitHub
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DijkstraQuery.php
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DijkstraQuery.php
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<?php
/**
* 迪克斯特拉算法
*
* @author Pu ShaoWei <pushaowei0727@gmail.com>
* @date 2017/8/23
* @license MIT
* -------------------------------------------------------------
* 思路分析：单源最短路径问题
* -------------------------------------------------------------
* Dijkstra 算法一般的表述通常有两种方式，一种用永久和临时标号方式，一种是用OPEN, CLOSE表的方式，
* 这里均采用永久和临时标号的方式。注意该算法要求图中不存在负权边。
* 因此，在包含负边全的图中要找出最短路径，可以使用另一种算法 -- 贝克曼-福德算法
*/
// +--------------------------------------------------------------------------
// | 解题方式
// +--------------------------------------------------------------------------
/**
* DijkstraQuery
*
* @uses PHPStorm
* @version 1.0
* @author Pu ShaoWei <pushaowei0727@gmail.com>
*/
class
DijkstraQuery
{
/**
* @var array
*/
protected
$
graph
;
/**
* @var array
*/
protected
$
processed
;
/**
* @var int
*/
protected
$
infinity
;
/**
* @var string
*/
protected
$
start
;
/**
* @var string
*/
protected
$
end
;
/**
* DijkstraQuery constructor.
*
* @param array $graph
* @param $start
* @param $end
*/
public
function
__construct
(
array
$
graph
,
$
start
,
$
end
)
{
$
this
->
graph
=
$
graph
;
$
this
->
start
=
$
start
;
$
this
->
end
=
$
end
;
$
this
->
processed
=
array
();
$
this
->
infinity
=
mt_getrandmax
();
}
/**
* 最短路径
*
* @return string
*/
public
function
calculate
()
{
$
costs
=
$
this
->
graph
[
$
this
->
start
];
$
costs
[
$
this
->
end
] =
$
this
->
infinity
;
$
node
=
$
this
->
findLowestCostNode
(
$
costs
);
while
(
null
!==
$
node
) {
$
cost
=
$
costs
[
$
node
];
$
neighbors
=
$
this
->
graph
[
$
node
] ??
array
();
foreach
(
$
neighbors
as
$
neighbor
=>
$
distance
) {
$
newCost
=
$
cost
+
$
distance
;
if
(
$
costs
[
$
neighbor
] >
$
newCost
) {
$
costs
[
$
neighbor
] =
$
newCost
;
}
}
array_push
(
$
this
->
processed
,
$
node
);
$
node
=
$
this
->
findLowestCostNode
(
$
costs
);
}
return
'
The shortest distance for：
'
.
$
costs
[
$
this
->
end
];
}
/**
* findLowestCostNode
*
* @param $costs
* @return null
*/
protected
function
findLowestCostNode
(
$
costs
)
{
$
lowestCost
=
$
this
->
infinity
;
$
lowestCostNode
=
null
;
foreach
(
$
costs
as
$
node
=>
$
cost
) {
if
(
$
cost
<
$
lowestCost
&& !
in_array
(
$
node
,
$
this
->
processed
)) {
$
lowestCost
=
$
cost
;
$
lowestCostNode
=
$
node
;
}
}
return
$
lowestCostNode
;
}
}
// +--------------------------------------------------------------------------
// | 验证 me --> claire
// +--------------------------------------------------------------------------
// ∞
$
graph
=
array
(
'
me
'
=>
array
(
'
alice
'
=>
6
,
'
bob
'
=>
2
,
),
'
alice
'
=>
array
(
'
claire
'
=>
1
,
),
'
bob
'
=>
array
(
'
alice
'
=>
3
,
'
claire
'
=>
5
,
),
'
claire
'
=>
array
(
// 没有任何邻居
),
);
echo
(
new
DijkstraQuery
(
$
graph
,
'
me
'
,
'
claire
'
))->
calculate
();
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