【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[0..200000]of longint;
    ch:array[1..200]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:=0 to n-1 do
 begin
  x[i]:=a[i];
  inc(wc[x[i]]);
 end;
 for i:=1 to m-1 do wc[i]:=wc[i-1]+wc[i];
 for i:=n-1 downto 0 do
 begin
  dec(wc[x[i]]);
  sa[wc[x[i]]]:=i;
 end;
 j:=1; p:=1;
 while p<n do
 begin
  p:=0;
  for i:=n-j to n-1 do
  begin
   y[p]:=i; inc(p);
  end;
  for i:=0 to n-1 do
   if sa[i]>=j then begin y[p]:=sa[i]-j; inc(p); end;
  for i:=0 to n-1 do wd[i]:=x[y[i]];
  for i:=0 to m-1 do wc[i]:=0;
  for i:=0 to n-1 do inc(wc[wd[i]]);
  for i:=1 to m-1 do wc[i]:=wc[i-1]+wc[i];
  for i:=n-1 downto 0 do
  begin
   dec(wc[wd[i]]);
   sa[wc[wd[i]]]:=y[i];
  end;
  for i:=0 to n do swap(x[i],y[i]);
  p:=1; x[sa[0]]:=0;
  for i:=1 to n-1 do
   if cmp(sa[i-1],sa[i],j) then x[sa[i]]:=p-1
    else begin x[sa[i]]:=p; inc(p); end;
  j:=j*2;
  m:=p;
 end;
end;

procedure getheight(n:longint);
var i,j,k:longint;
begin
 for i:=1 to n do rank[sa[i]]:=i;
 k:=0;
 for i:=0 to n-1 do
 begin
  if k>0 then dec(k);
  j:=sa[rank[i]-1];
  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:=1 to n1 do flag[i]:=1;
 cnt:=0; s:=0;
 for i:=1 to n do
  if height[i]>=x then
  begin
   cnt:=cnt+flag[b[sa[i]]]; flag[b[sa[i]]]:=0;
   cnt:=cnt+flag[b[sa[i-1]]]; flag[b[sa[i-1]]]:=0;
  end
   else
   begin
    if cnt>n1 div 2 then begin inc(s); ans[s]:=sa[i-1]; end;
    cnt:=0;
    for j:=1 to n1 do flag[j]:=1;
   end;
 if cnt>n1 div 2 then begin inc(s); ans[s]:=sa[n]; end;
 if s>0 then
 begin
  ans[0]:=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),0);
 fillchar(b,sizeof(b),0);
 fillchar(x,sizeof(x),0);
 fillchar(y,sizeof(y),0);
 fillchar(sa,sizeof(sa),0);
 fillchar(rank,sizeof(rank),0);
 fillchar(ans,sizeof(ans),0);
 fillchar(wc,sizeof(wc),0);
 fillchar(wd,sizeof(wd),0);
 fillchar(height,sizeof(height),0);
end;

begin
 assign(input,'poj3294.in'); reset(input);
 assign(output,'poj3294.out'); rewrite(output);
 while not eof do
 begin
  init;
  readln(n1);
  if n1=0 then break;
  n:=0;
  for i:=1 to n1 do
  begin
   readln(ch[i]);
   len:=length(ch[i]);
   for j:=n to n+len-1 do
   begin
    a[j]:=ord(ch[i][j-n+1])+100;
    b[j]:=i;
   end;
   n:=n+len; a[n]:=i;
   inc(n);
  end;
  dec(n); a[n]:=0; m:=300;
  getsa(n+1);
  getheight(n);

  l:=1; r:=n; last:=0;
  while l<=r do
  begin
   mid:=(l+r)>>1;
   if isok(mid) then begin last:=mid; l:=mid+1; end
    else r:=mid-1;
  end;
  if last=0 then writeln('?')
   else
   begin
    for i:=1 to ans[0] do
    begin
     for j:=ans[i] to ans[i]+last-1 do write(chr(a[j]-100));
     writeln;
    end;
   end;
  writeln;
 end;
 close(input);
 close(output);
end.