poj3294

【题意】

n个字符串，求最长的出现在多于一半字符串中的子串

【输入】

多组数据

每组第一行一个n表示n个字符串

接下来n行是n个字符串

【输出】

对于每组答案，输出最长的出现在多于一半字符串中的子串，如有多个，按字典序输出

若不存在，则输出'?'

两组数据答案之间用空行分隔

后缀数组经典运用之一

二分答案，然后按height分组，看每组来自多少个不同的字符串

注意n=1的情况

program poj3294;var  n,m,i,j,k,tot,ans,s,e,mid,limit,max:longint;  ok:boolean;  root,temp:ansistring;  belong,change,total,dl,now,keep,rank,sa,height:array [-1..110001] of longint;  yes:array [0..1001] of boolean;  fin:array [0..1001] of longint;procedure swap (var a,b:longint);var  i:longint;begin  i:=a;  a:=b;  b:=i;end;procedure qsort (s,e:longint);var  i,j,k:longint;begin  if s>=e then exit;  i:=s;  j:=e;  k:=dl[(s+e) div 2];  while i<=j do    begin       while root[dl[i]]<root[k] do inc(i);       while root[dl[j]]>root[k] do dec(j);       if i>j then break;       swap(dl[i],dl[j]);       inc(i);       dec(j);    end;  qsort(s,j);  qsort(i,e);end;function search (mid:longint):boolean;begin  search:=false;  tot:=0;  fillchar(yes,sizeof(yes),false);  k:=1;  yes[belong[sa[m+1]]]:=true;  for i:=m+2 to n do    begin      if (height[i]<mid)or(fin[belong[sa[i]]]-sa[i]<mid) then        begin          if k>=limit then            begin              search:=true;              inc(tot);              dl[tot]:=sa[i-1];            end;          k:=1;          fillchar(yes,sizeof(yes),false);          yes[belong[sa[i]]]:=true;          continue;        end;      if not yes[belong[sa[i]]] then        begin          yes[belong[sa[i]]]:=true;          inc(k);        end;    end;  if k>=limit then    begin      search:=true;      inc(tot);      dl[tot]:=sa[i-1];    end;end;begin  repeat    readln(m);    if m=0 then break;    if m and 1 = 1 then limit:=m-m div 2                   else limit:=m div 2 + 1;    root:='';    max:=maxlongint;    for i:=1 to m do      begin        readln(temp);        if length(temp)<max then max:=length(temp);        root:=root+temp+' ';      end;    if m=1 then      begin        writeln(temp);        writeln;        continue;      end;    n:=length(root);    for i:=1 to n do      dl[i]:=i;    qsort(1,n);    k:=1;    for i:=1 to n do      begin        if root[dl[i]]<>root[dl[k]] then k:=i;        rank[dl[i]]:=k;      end;    k:=0;    while 1 shl k<n do      begin        for i:=1 to n do          if i+(1 shl k)>n then change[i]:=0                           else change[i]:=rank[i+(1 shl k)];        fillchar(total,sizeof(total),0);        for i:=1 to n do          inc(total[change[i]]);        for i:=1 to n do          total[i]:=total[i]+total[i-1];        for i:=1 to n do          begin            dl[total[change[i]-1]+1]:=i;            inc(total[change[i]-1]);          end;        fillchar(total,sizeof(total),0);        for i:=1 to n do          inc(total[rank[i]]);        for i:=2 to n do          total[i]:=total[i]+total[i-1];        fillchar(now,sizeof(now),0);        fillchar(keep,sizeof(keep),0);        for i:=1 to n do          begin            if now[rank[dl[i]]]<>change[dl[i]] then              begin                now[rank[dl[i]]]:=change[dl[i]];                total[rank[dl[i]]-1]:=total[rank[dl[i]]-1]+keep[rank[dl[i]]];                keep[rank[dl[i]]]:=0;              end;            inc(keep[rank[dl[i]]]);            rank[dl[i]]:=total[rank[dl[i]]-1]+1;          end;        inc(k);      end;    for i:=1 to n do      sa[rank[i]]:=i;    fillchar(height,sizeof(height),0);    for i:=1 to n do      begin        if rank[i]=1 then continue;        k:=height[rank[i-1]]-1;        if k<0 then k:=0;        while (i+k<=n)and(sa[rank[i]-1]+k<=n)        and(root[i+k]=root[sa[rank[i]-1]+k]) do inc(k);        height[rank[i]]:=k;      end;    k:=1;    for i:=1 to n do      if root[i]=' ' then        begin          fin[k]:=i;          inc(k);        end                     else belong[i]:=k;    s:=0;    e:=max;    while s<>e do      begin        mid:=s+e-(s+e) div 2;        if search(mid) then s:=mid                       else e:=mid-1;      end;    if s=0 then      begin        writeln('?');        writeln;        continue;      end;    ok:=search(s);    for i:=1 to tot do      writeln(copy(root,dl[i],s));    writeln;  until false;end.