Dijkstra's algorithm: Difference between revisions
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Line 3,302:
5: distance = 11, 0 --> 2 --> 5
</pre>
=={{header|EasyLang}}==
<syntaxhighlight>
global con[][] n .
proc read . .
repeat
s$ = input
until s$ = ""
a = (strcode substr s$ 1 1) - 96
b = (strcode substr s$ 3 1) - 96
d = number substr s$ 5 9
if a > len con[][]
len con[][] a
.
con[a][] &= b
con[a][] &= d
.
con[][] &= [ ]
n = len con[][]
.
read
#
len cost[] n
len prev[] n
#
proc dijkstra . .
for i = 2 to len cost[]
cost[i] = 1 / 0
.
len todo[] n
todo[1] = 1
repeat
min = 1 / 0
a = 0
for i to len todo[]
if todo[i] = 1 and cost[i] < min
min = cost[i]
a = i
.
.
until a = 0
todo[a] = 0
for i = 1 step 2 to len con[a][] - 1
b = con[a][i]
c = con[a][i + 1]
if cost[a] + c < cost[b]
cost[b] = cost[a] + c
prev[b] = a
todo[b] = 1
.
.
.
.
dijkstra
#
func$ gpath nd$ .
nd = strcode nd$ - 96
while nd <> 1
s$ = " -> " & strchar (nd + 96) & s$
nd = prev[nd]
.
return "a" & s$
.
print gpath "e"
print gpath "f"
#
input_data
a b 7
a c 9
a f 14
b c 10
b d 15
c d 11
c f 2
d e 6
e f 9
</syntaxhighlight>
=={{header|Emacs Lisp}}==
Line 3,482 ⟶ 3,560:
Some [A; C; F]
</pre>
=={{header|Forth}}==
{{trans|Commodore BASIC}}
<syntaxhighlight lang="FORTH">\ utility routine to increment a variable
: 1+! 1 swap +! ;
\ edge data
variable edge-count
0 edge-count !
create edges
'a , 'b , 7 , edge-count 1+!
'a , 'c , 9 , edge-count 1+!
'a , 'f , 14 , edge-count 1+!
'b , 'c , 10 , edge-count 1+!
'b , 'd , 15 , edge-count 1+!
'c , 'd , 11 , edge-count 1+!
'c , 'f , 2 , edge-count 1+!
'd , 'e , 6 , edge-count 1+!
'e , 'f , 9 , edge-count 1+!
\ with accessors
: edge 3 * cells edges + ;
: edge-from edge ;
: edge-to edge 1 cells + ;
: edge-weight edge 2 cells + ;
\ vertex data and acccessor
create vertex-names edge-count @ 2 * cells allot
: vertex-name cells vertex-names + ;
variable vertex-count
0 vertex-count !
\ routine to look up a vertex by name
: find-vertex
-1 swap
vertex-count @ 0 ?do
dup i vertex-name @ = if swap drop i swap leave then
loop
drop
;
\ routine to add a new vertex name if not found
: add-vertex
dup find-vertex dup -1 = if
swap vertex-count @ vertex-name !
vertex-count dup @ swap 1+!
swap drop
else
swap
drop
then
;
\ routine to add vertices to name table and replace names with indices in edges
: get-vertices
edge-count @ 0 ?do
i edge-from @ add-vertex i edge-from !
i edge-to @ add-vertex i edge-to !
loop
;
\ call it
get-vertices
\ variables to hold state during algorithm run
create been-visited
vertex-count @ cells allot
: visited cells been-visited + ;
create prior-vertices
vertex-count @ cells allot
: prior-vertex cells prior-vertices + ;
create distances
vertex-count @ cells allot
: distance cells distances + ;
variable origin
variable current-vertex
variable neighbor
variable current-distance
variable tentative
variable closest-vertex
variable minimum-distance
variable vertex
\ call with origin vertex name on stack
: dijkstra ( origin -- )
find-vertex origin !
been-visited vertex-count @ cells 0 fill
prior-vertices vertex-count @ cells -1 fill
distances vertex-count @ cells -1 fill
0 origin @ distance ! \ distance to origin is 0
origin @ current-vertex ! \ current vertex is the origin
begin
edge-count @ 0 ?do
i edge-from @ current-vertex @ = if \ if edge is from current
i edge-to @ neighbor ! \ neighbor vertex
neighbor @ distance @ current-distance !
current-vertex @ distance @ i edge-weight @ + tentative !
current-distance @ -1 = tentative @ current-distance @ < or if
tentative @ neighbor @ distance !
current-vertex @ neighbor @ prior-vertex !
then
else
then
loop
1 current-vertex @ visited ! \ current vertex has now been visited
-1 closest-vertex !
vertex-count @ 0 ?do
i visited @ 0= if
-1 minimum-distance !
closest-vertex @ dup -1 <> if
distance @ minimum-distance !
else
drop
then
i distance @ -1 <>
minimum-distance @ -1 = i distance @ minimum-distance @ < or
and if
i closest-vertex !
then
then
loop
closest-vertex @ current-vertex !
current-vertex @ -1 = until
cr
." Shortest path to each vertex from " origin @ vertex-name @ emit ': emit cr
vertex-count @ 0 ?do
i origin @ <> if
i vertex-name @ emit ." : " i distance @ dup
-1 = if
drop
." ∞ (unreachable)"
else
.
'( emit
i vertex !
begin
vertex @ vertex-name @ emit
vertex @ origin @ <> while
." ←"
vertex @ prior-vertex @ vertex !
repeat
') emit
then
cr
then
loop
;</syntaxhighlight>
{{Out}}
<pre>'a dijkstra
Shortest path to each vertex from a:
b: 7 (b←a)
c: 9 (c←a)
f: 11 (f←c←a)
d: 20 (d←c←a)
e: 26 (e←d←c←a)
ok
'b dijkstra
Shortest path to each vertex from b:
a: ∞ (unreachable)
c: 10 (c←b)
f: 12 (f←c←b)
d: 15 (d←b)
e: 21 (e←d←b)
ok</pre>
=={{header|Fortran}}==
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