bzoj2797

对和排序，显然最小是a1+a2,次小a1+a3 然后穷举哪里是a2+a3 这样a1,a2,a3就求出来了

注意a2+a3只可能是前n+1项中的一个，所以穷举这步是O(n)的

接下来我们把已经确定的数的和找到并标记，那么下一个未标记的和就是a1+新的数，然后依次递推下去即可

 var v:array[..] of boolean;
     a:array[..] of longint;
     b:array[..] of longint;
     ans:array[..,..] of longint;
     i,j,n,m,t:longint;

 procedure swap(var a,b:longint);
   var c:longint;
   begin
     c:=a;
     a:=b;
     b:=c;
   end;

 procedure sort(l,r:longint);
   var i,j,x:longint;
   begin
     i:=l;
     j:=r;
     x:=a[(l+r) shr ];
     repeat
       while a[i]<x do inc(i);
       while x<a[j] do dec(j);
       if not(i>j) then
       begin
         swap(a[i],a[j]);
         inc(i);
         dec(j);
       end;
     until i>j;
     if l<j then sort(l,j);
     if i<r then sort(i,r);
   end;

 function find(l,r,x:longint):longint;
   var m:longint;
   begin
     while l<=r do
     begin
       m:=(l+r) shr ;
       if a[m]=x then exit(m);
       if a[m]>x then r:=m- else l:=m+;
     end;
     exit(-);
   end;

 procedure check(i:longint);
   var j,k,p,x,y:longint;
   begin
     fillchar(v,sizeof(v),false);
     fillchar(b,sizeof(b),);
     if (a[]+a[]-a[i]) mod <> then exit;
     b[]:=(a[]+a[]-a[i]) div ;
     b[]:=a[]-b[];
     b[]:=a[]-b[];
     v[]:=true; v[]:=true; v[i]:=true;
     p:=;
     for j:= to n do
     begin
       while (p<=m) and v[p] do inc(p);
       if p>m then exit;
       b[j]:=a[p]-b[];
       v[p]:=true;
       for k:= to j- do
       begin
         if b[k]>=b[j] then exit;
         x:=find(,m,b[k]+b[j]);
         if x=- then exit;
         y:=x;
         while (y>) and (a[y]=a[x]) do dec(y);
         inc(y);
         while (y<=m) and (a[y]=a[x]) and v[y] do inc(y);
         if (y>m) or (a[y]<>a[x]) or v[y] then exit;
         v[y]:=true;
       end;
     end;
     inc(t);
     ans[t]:=b;
   end;

 begin
   readln(n);
   m:=(n-)*n div ;
   for i:= to m do
     read(a[i]);
   sort(,m);
   for i:= to n+ do
     if a[i]<>a[i-] then check(i);
   writeln(t);
   for i:= to t do
   begin
     for j:= to n do
       write(ans[i,j],' ');
     writeln;
   end;
 end.