| 1 | /* A program to solve the 8-queens problem */ |
| 2 | |
| 3 | let |
| 4 | var N := 8 |
| 5 | |
| 6 | type intArray = array of int |
| 7 | |
| 8 | var row := intArray [ N ] of 0 |
| 9 | var col := intArray [ N ] of 0 |
| 10 | var diag1 := intArray [N+N-1] of 0 |
| 11 | var diag2 := intArray [N+N-1] of 0 |
| 12 | |
| 13 | function printboard() = ( |
| 14 | for i := 0 to N-1 do ( |
| 15 | for j := 0 to N-1 do print(if col[i]=j then " O" else " ."); |
| 16 | print("\n") |
| 17 | ); |
| 18 | print("\n") |
| 19 | ) |
| 20 | |
| 21 | function try(c:int) = ( |
| 22 | /* for i:= 0 to c do print("."); print("\n"); flush();*/ |
| 23 | if c=N |
| 24 | then printboard() |
| 25 | else |
| 26 | for r := 0 to N-1 |
| 27 | do |
| 28 | if row[r]=0 & diag1[r+c]=0 & diag2[r+7-c]=0 |
| 29 | then ( |
| 30 | row[r] := 1; |
| 31 | diag1[r+c] := 1; |
| 32 | diag2[r+7-c] := 1; |
| 33 | col[c] := r; |
| 34 | try(c+1); |
| 35 | row[r] := 0; |
| 36 | diag1[r+c] := 0; |
| 37 | diag2[r+7-c] := 0 |
| 38 | ) |
| 39 | ) |
| 40 | in |
| 41 | try(0) |
| 42 | end |