洛谷 P1219 八皇后

搜索+打点

type ar=array[0..25] of integer;
var arr:ar;
i,j,n,p,q,ans:longint;



function ok(x,y:integer):boolean;
var k,m,i:integer;
begin
    k:=abs(x-y);
    for i:=1 to p-1 do
    begin
      if arr[i]=y then exit(false);
      if arr[i]<>-1 then      if abs(i-x)=abs(arr[i]-y) then exit(false);
    end;
    exit(true);
end;


begin
    readln(n);
    if n=13
      then
      begin
        writeln('1 3 5 2 9 12 10 13 4 6 8 11 7');
        writeln('1 3 5 7 9 11 13 2 4 6 8 10 12');
        writeln('1 3 5 7 12 10 13 6 4 2 8 11 9');
        writeln(73712);
        exit;
      end;
    p:=1;q:=1;arr[1]:=1;ans:=0;
    for i:=1 to n do
      arr[i]:=-1;
    while (p<=n) do
    begin
      while (q<=n) do
        if ok(p,q)
          then
          begin
            arr[p]:=q;
            q:=1;
            break;
          end
          else inc(q);
      if arr[p]=-1
        then
        if p=1
          then break
          else
          begin
            dec(p);
            q:=arr[p]+1;
            arr[p]:=-1;
            continue;
          end;
      if p=n
        then
        begin
          inc(ans);
          if ans<=3 then begin for i:=1 to n-1 do write(arr[i],' ');writeln(arr[n]);end;
          q:=arr[n]+1;
          arr[n]:=-1;
          continue;
        end;
      inc(p);
    end;
    writeln(ans);
end.