1509 -- Glass Beads POJ

题意：求一个字符串的最小表示的开始下标

就当模板题写了

把字符串重复一遍，再建后缀自动机，贪心的选最小字典序在上面走len步

因为走出来的一定是子串，长度又是len，所以一定是原来的字符串旋转得到的，就解决了

 

 1 const

 2     maxn=50010;

 3 type

 4     node=record

 5       go:array[0..25]of longint;

 6       step,fa:longint;

 7     end;

 8 

 9 var

10     sam:array[0..maxn]of node;

11     s,ans:ansistring;

12     len,tot,last,t:longint;

13 

14 procedure add(x:longint);

15 var

16     now,new,q:longint;

17 begin

18     inc(tot);

19     now:=tot;

20     fillchar(sam[now].go,sizeof(sam[now].go),0);

21     sam[now].step:=sam[last].step+1;

22     while (last<>0)and(sam[last].go[x]=0) do

23       begin

24         sam[last].go[x]:=now;

25         last:=sam[last].fa;

26       end;

27     if last=0 then sam[now].fa:=1

28     else

29       begin

30         q:=sam[last].go[x];

31         if sam[q].step=sam[last].step+1 then sam[now].fa:=q

32         else

33           begin

34             inc(tot);

35             new:=tot;

36             sam[new]:=sam[q];

37             sam[q].fa:=new;

38             sam[now].fa:=new;

39             sam[new].step:=sam[last].step+1;

40             while (last<>0)and(sam[last].go[x]=q) do

41               begin

42                 sam[last].go[x]:=new;

43                 last:=sam[last].fa;

44               end;

45           end;

46       end;

47     last:=now;

48 end;

49 

50 procedure main;

51 var

52     i,j,k:longint;

53 begin

54     readln(s);

55     s:=s+s;

56     len:=length(s);

57     last:=1;

58     tot:=1;

59     sam[1].fa:=0;

60     sam[1].step:=0;

61     fillchar(sam[1].go,sizeof(sam[1].go),0);

62     for i:=1 to len do

63       add(ord(s[i])-ord('a'));

64     i:=1;

65     j:=0;

66     ans:='';

67     while j<len>>1 do

68       begin

69         inc(j);

70         for k:=0 to 25 do

71           if sam[i].go[k]<>0 then break;

72         ans:=ans+chr(k+ord('a'));

73         i:=sam[i].go[k];

74       end;

75     writeln(pos(ans,s));

76 end;

77 

78 begin

79     readln(t);

80     while t<>0 do

81       begin

82         main;

83         dec(t);

84       end;

85 end.

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