(*===================================================================*)
(* Pascal program for distribution from the Combinatorial Object *)
(* Server. Generate permutations in lexicographic order. This is *)
(* the same version used in the book "Combinatorial Generation." *)
(* The program can be modified, translated to other languages, etc., *)
(* so long as proper acknowledgement is given (author and source). *)
(* Programmer: Joe Sawada, 1997. *)
(* The latest version of this program may be found at the site *)
(* http://theory.cs.uvic.ca/inf/perm/PermInfo.html *)
(*===================================================================*)
program Permlex (input, output);
var
n : integer;
i : integer;
a : array [0..100] of integer; { The permutation }
procedure PrintPerm;
var j:integer;
begin
for j:=1 to n do write(a[j]:1);
writeln;
end;
procedure swap(i:integer; j:integer);
var temp : integer;
begin
temp := a[i];
a[i] := a[j];
a[j] := temp;
end;
function Next : integer;
var k,j,r,s : integer;
begin
k := n-1;
while a[k] > a[k+1] do k:=k-1;
if k = 0 then Next:=0
else begin
j := n;
while a[k] > a[j] do j:=j-1;
swap(j,k);
r:=n;
s:=k+1;
while r>s do begin
swap(r,s);
r:=r-1;
s:=s+1;
end;
Next:=1;
PrintPerm();
end;
end;
begin
write('Enter n: '); readln(n);
writeln;
if n > 0 then begin
for i := 0 to n do a[i] := i;
PrintPerm;
while (Next = 1) do ;
writeln;
end;
readln;
end.
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