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Just another update

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Ingy döt Net 2015-02-20 00:35:01 -05:00
parent a25938f123
commit 00a190b0a6
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Task/N-queens-problem/REXX/n-queens-problem.rexx
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@ -1,64 +1,51 @@
/*REXX program place N queens on a NxN chessboard (the 8 queens problem)*/
/*REXX program places N queens on a NxN chessboard; the 8 queens problem*/
parse arg N . /*get board size arg (if any). */
if N=='' then N=8 /*No argument? Use the default.*/
file=1; rank=1; q=0 /*starting place, # of queens. */
if N=='' then N=8; if N<1 then call noSol /*No arg? Use the default.*/
rank=1; file=1; q=0 /*starting rank & file; # queens.*/
@.=0; !=left('', 9* (N<18)) /*define empty board, indentation*/
/*═════════════════════════════════════find solution: N queens problem.*/
do while q<N /*keep placing queens until done.*/
@.file.rank=1 /*place a queen on the chessboard*/
do while q<N; @.file.rank=1 /*keep placing queens until done.*/
if safe?(file,rank) then do; q=q+1 /*if not being attacked, eureka! */
file=1 /*another attempt at file #1, */
file=1 /*another attempt at another file*/
rank=rank+1 /*and also bump the rank pointer.*/
end
else do /*¬ safe, so it's a bad placement*/
@.file.rank=0 /* So, remove this queen. */
file=file+1 /*try the next file then. */
do while file>N; rank=rank-1
if rank==0 then call noSol
do j=1 for N
if @.j.rank then do; file=j; @.file.rank=0
q=q-1; file=j+1
leave /*j*/
end
end /*j*/
end /*do while file>N*/
end /*else do*/
end /*while q<N*/
iterate /*go&try another queen placement.*/
end /* [↑] found a good Q placement.*/
@.file.rank=0 /*not safe, so remove this queen.*/
file=file+1 /*So, try the next (higher) file.*/
do while file>N; rank=rank-1; if rank==0 then call noSol
do j=1 for N; if \@.j.rank then iterate /*occupied?*/
file=j; @.file.rank=0; q=q-1; file=j+1; leave /*j*/
end /*j*/
end /*while file>N*/
end /*while q<N*/
/*══════════════════════════════════════show chessboard with a solution.*/
say 'A solution for' N "queens:"; _ = substr( copies("┼───", N) ,2)
say 'A solution for' N "queens:"; _ = substr( copies("┼───", N) ,2)
lineT = '┌'_"┐"; say; say ! translate(lineT,'┬',"┼")
lineB = '└'_"┘"; lineB = translate(lineB, '┴', "┼")
line = '├'_"┤" /*define a line for cell boundry.*/
bar = '│' /*kinds: horizonal/vertical/salad*/
Bqueen = '░♀░' /*glyph befitting the black queen*/
Wqueen = ' ♀ ' /* " " " white " */
/*═══════════════════════==══════════════place the queens on chessboard.*/
do r=1 for N; if r\==1 then say ! line; _= /*process the rank &*/
if 1=='f1'x then do; queenSymbol='Q'; dither='9c'x; end /*for EBCDIC.*/
else do; queenSymbol='♀'; dither='b0'x; end /* " ASCII.*/
Bqueen = dither||queenSymbol||dither /*glyph befitting the black queen*/
Wqueen = ' 'queenSymbol" " /* " " " white " */
/*═══════════════════════════════════════show chessboard with the queens*/
do r=1 for N; if r\==1 then say ! line; _= /*process the rank &*/
do f=1 for N; black=(f+r)//2 /*the file; is it a black square?*/
qgylph=Wqueen; if black then Qgylph=Bqueen /*use a black queen.*/
Qgylph=Wqueen; if black then Qgylph=Bqueen /*use a black queen.*/
/*is it black sqare?*/
if @.f.r then _=_ || bar || Qgylph /*use the 3-char symbol for queen*/
else if black then _=_ || bar'░░░' /*¼ dithering char. */
else _=_ || bar' ' /*three blanks. */
else if black then _=_||bar||copies(dither,3) /*dithering.*/
else _=_||bar' ' /*3 blanks. */
end /*f*/ /* [↑] preserve square chessboard*/
say ! _ || bar
say ! _ || bar /*show a rank of the chessboard. */
end /*r*/ /*80 cols can view 19x19 chessbrd*/
say ! lineB; say /*show last line, + a blank line.*/
exit 1 /*stick a fork in it, we're done.*/
/*──────────────────────────────────NOSOL subroutine────────────────────*/
noSol: say "No solution for" N 'queens.'; exit 0
/*──────────────────────────────────SAFE? subroutine────────────────────*/
safe?: procedure expose @.; parse arg file,rank
do k=rank-1 to 1 by -1; if @.file.k then return 0
end
f=file-1; r=rank-1
do while f\==0 & r\==0; if @.f.r then return 0
f=f-1; r=r-1
end
f=file+1; r=rank-1
do while f<=n & r\==0; if @.f.r then return 0
f=f+1; r=r-1
end
safe?: procedure expose @. N; parse arg f,r; rm=r-1; fm=f-1; fp=f+1
do k=1 for rm; if @.f.k then return 0; end
f=fm; do k=rm by -1 for rm while f\==0; if @.f.k then return 0; f=f-1; end
f=fp; do k=rm by -1 for rm while f <=N; if @.f.k then return 0; f=f+1; end
return 1