Question

How to write a recursive function to generate all permutations of a string in Pascal

Answer 1

program PermuteString;

procedure Swap(var a, b: char);
var
  temp: char;
begin
  temp := a;
  a := b;
  b := temp;
end;

procedure generatePermutation(var str: string; l, r: integer);
var
  i: integer;
begin
  if l = r then
    writeln(str)
  else
    for i := l to r do
    begin
      Swap(str[l + 1], str[i + 1]); 
      generatePermutation(str, l + 1, r);
      Swap(str[l + 1], str[i + 1]);  // backtrack
    end;
end;

var
  s: string;
begin
  s := 'ABC';
  generatePermutation(s, 0, Length(s) - 1);
end.



(*
run:

ABC
ACB
BAC
BCA
CBA
CAB

*)

 

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