var
  g:array[1..1000,1..1000] of Boolean;
  i,j,n,a,k,s:smallint;
procedure find(i:smallint);
var
  j:smallint;
begin
  for j:=n downto 1 do
    if g[i,j] then
      begin
        g[i,j]:=false;
        find(j)
      end;
  if s<>0 then
    writeln(s,' ',i);
  s:=i;
end;
begin
  assign(input,'');
  reset(input);
  readln(n,a);
  for i:=1 to n do
    for j:=1 to n do
      begin
        read(k);
        g[i,j]:=(k=0) and (i<>j)
      end;
  close(input);
  s:=0;
  find(a);
end.

If I put s in memory and write it in reverse order I get MLE on test 12:
var
  g:array[1..1000,1..1000] of Boolean;
  i,j,n,a,k,st:smallint;
  s:array[1..32000] of smallint;
procedure find(i:smallint);
var
  j:smallint;
begin
  for j:=n downto 1 do
    if g[i][j] then
      begin
        g[i][j]:=false;
        find(j)
      end;
  inc(st);
  s[st]:=i
end;
begin
  assign(input,'');
  reset(input);
  readln(n,a);
  for i:=1 to n do
    for j:=1 to n do
      begin
        read(k);
        g[i][j]:=(k=0) and (i<>j)
      end;
  close(input);
  st:=0;
  find(a);
  for i:=st-1 downto 1 do
    writeln(s[i+1],' ',s[i]);
end.

Please help me solve either of this two problems.

There are two way to accept it:
1. Use stack instead of recursion.
2. Use recursion without variable "j".

In all cases you can use array "st" and don't worry about memory limit.

you can use dynamic lists for the graph instead of that bool matrix...