Programming Languages (CS302 2007S)

Algorithm 306: Permutation with Repetitions

A reformatted version of:

Bratley, P. (1967). Algorithm 306: Permutation with Repetitions [G6]. Communications of the ACM 10(7), July 1967, pp. 450-451.

procedure perm(a, n, last);
     value n;
     integer n;
     integer array a;
     Boolean last;
begin
     integer i, p, q, r;
     own integer m;
     own integer array b[1:n];
     if (!last) then go to L12;
     last := false;
     for i := 1 step 1 until n do b[i] := a[i];
     p := b[n];
     for i := n step -1 until 1 do
       if p != b[i] then
         begin m := i; go to L99 end;
     m := 0;
     go to L99;
L12: if m = 0 then go to L10;
     p := b[m]; q := m; r := 0;
L9:  i := n;
L4:  if a[i] = p then go to L2
     if a[i] < p then r := i;
L5:  i := i-1; go to L4
L2:  a[i] := b[n] - 1;
     if r = 0 then go to L8
L1:  a[r] := p; q := q+1;
L3:  r := r+1;
     if r > n then go to L11
     else if a[r] > p then go to L3
L11: if b[q] = p then go to L1
     r := 0;
L6:  r := r+1; 
     if a[r] >= p then go to L6;
     a[r] := b[q];
     if q=n then go to L7;
     q := q + 1;
     go to L6;
L7:  last := false; go to L99;
L8:  q := q - 1; 
     if q = 0 then go to L10;
     if b[q] = p then go to L5;
     p := b[q]; go to L9;
L10:  last := true;
L99: 
end perm

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This document was generated by Siteweaver on Mon Jan 29 08:26:34 2007.
The source to the document was last modified on Mon Jan 29 08:26:33 2007.
This document may be found at http://www.cs.grinnell.edu/~rebelsky/Courses/CS302/2007S/Examples/permrep.html.

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Samuel A. Rebelsky, rebelsky@grinnell.edu