【POJ3294】Life Forms（后缀数组，二分）

题意：

n<=100 len[i]<=1000

思路：这是一道论文题

 var a,x,y,sa,rank,height,wc,wd,ans,flag,b:array[..]of longint;
     ch:array[..]of ansistring;
     n,n1,l,r,mid,last,i,j,m,len:longint;

 procedure swap(var x,y:longint);
 var t:longint;
 begin
  t:=x; x:=y; y:=t;
 end;

 function cmp(a,b,l:longint):boolean;
 begin
  exit((y[a]=y[b])and(y[a+l]=y[b+l]));
 end;

 procedure getsa(n:longint);
 var i,j,p:longint;
 begin
  for i:= to n- do
  begin
   x[i]:=a[i];
   inc(wc[x[i]]);
  end;
  for i:= to m- do wc[i]:=wc[i-]+wc[i];
  for i:=n- downto  do
  begin
   dec(wc[x[i]]);
   sa[wc[x[i]]]:=i;
  end;
  j:=; p:=;
  while p<n do
  begin
   p:=;
   for i:=n-j to n- do
   begin
    y[p]:=i; inc(p);
   end;
   for i:= to n- do
    if sa[i]>=j then begin y[p]:=sa[i]-j; inc(p); end;
   for i:= to n- do wd[i]:=x[y[i]];
   for i:= to m- do wc[i]:=;
   for i:= to n- do inc(wc[wd[i]]);
   for i:= to m- do wc[i]:=wc[i-]+wc[i];
   for i:=n- downto  do
   begin
    dec(wc[wd[i]]);
    sa[wc[wd[i]]]:=y[i];
   end;
   for i:= to n do swap(x[i],y[i]);
   p:=; x[sa[]]:=;
   for i:= to n- do
    if cmp(sa[i-],sa[i],j) then x[sa[i]]:=p-
     else begin x[sa[i]]:=p; inc(p); end;
   j:=j*;
   m:=p;
  end;
 end;

 procedure getheight(n:longint);
 var i,j,k:longint;
 begin
  for i:= to n do rank[sa[i]]:=i;
  k:=;
  for i:= to n- do
  begin
   if k> then dec(k);
   j:=sa[rank[i]-];
   while a[i+k]=a[j+k] do inc(k);
   height[rank[i]]:=k;
  end;
 end;

 function isok(x:longint):boolean;
 var i,j,cnt,s:longint;
 begin
  for i:= to n1 do flag[i]:=;
  cnt:=; s:=;
  for i:= to n do
   if height[i]>=x then
   begin
    cnt:=cnt+flag[b[sa[i]]]; flag[b[sa[i]]]:=;
    cnt:=cnt+flag[b[sa[i-]]]; flag[b[sa[i-]]]:=;
   end
    else
    begin
     if cnt>n1 div  then begin inc(s); ans[s]:=sa[i-]; end;
     cnt:=;
     for j:= to n1 do flag[j]:=;
    end;
  if cnt>n1 div  then begin inc(s); ans[s]:=sa[n]; end;
  if s> then
  begin
   ans[]:=s;
   exit(true);
  end;
  exit(false);
 end;

 procedure init;
 var i:longint;
 begin
  {for i:=0 to n+1 do
  begin
   a[i]:=0; x[i]:=0; y[i]:=0;
   sa[i]:=0; rank[i]:=0; ans[i]:=0;
   wc[i]:=0; wd[i]:=0; b[i]:=0;
   height[i]:=0;
  end;             }
  fillchar(a,sizeof(a),);
  fillchar(b,sizeof(b),);
  fillchar(x,sizeof(x),);
  fillchar(y,sizeof(y),);
  fillchar(sa,sizeof(sa),);
  fillchar(rank,sizeof(rank),);
  fillchar(ans,sizeof(ans),);
  fillchar(wc,sizeof(wc),);
  fillchar(wd,sizeof(wd),);
  fillchar(height,sizeof(height),);
 end;

 begin
  assign(input,'poj3294.in'); reset(input);
  assign(output,'poj3294.out'); rewrite(output);
  while not eof do
  begin
   init;
   readln(n1);
   if n1= then break;
   n:=;
   for i:= to n1 do
   begin
    readln(ch[i]);
    len:=length(ch[i]);
    for j:=n to n+len- do
    begin
     a[j]:=ord(ch[i][j-n+])+;
     b[j]:=i;
    end;
    n:=n+len; a[n]:=i;
    inc(n);
   end;
   dec(n); a[n]:=; m:=;
   getsa(n+);
   getheight(n);

   l:=; r:=n; last:=;
   while l<=r do
   begin
    mid:=(l+r)>>;
    if isok(mid) then begin last:=mid; l:=mid+; end
     else r:=mid-;
   end;
   if last= then writeln('?')
    else
    begin
     for i:= to ans[] do
     begin
      for j:=ans[i] to ans[i]+last- do write(chr(a[j]-));
      writeln;
     end;
    end;
   writeln;
  end;
  close(input);
  close(output);
 end.