bzoj 3998: [TJOI2015]弦论(后缀自动机)

 1 #include<cstdio>
 2 #include<cstring>
 3 #define F(i,a,b) for(int i=a;i<=b;++i)
 4 #define mst(a,b) memset(a,b,sizeof(a))
 5 using namespace std;
 6 
 7 const int N=5e5+7,tyn=26,M=N*2;
 8 struct SAM{
 9     int tr[M][tyn],f[M],ml[M],ed,last,p,x,r,q;
10     int cnt[M],b[M],d[M];
11     inline int gid(char x){return x-‘a‘;}
12     inline void nc(int s,int &p){
13         ml[p=++ed]=s,f[ed]=cnt[ed]=0,mst(tr[ed],0);
14     }
15     void clear(){ed=0,nc(0,last);}
16     void add(int w){
17         nc(ml[x=last]+1,p),last=p,cnt[p]=1;
18         while(x&&!tr[x][w])tr[x][w]=p,x=f[x];
19         if(!x)f[p]=1;
20         else if(ml[x]+1==ml[q=tr[x][w]])f[p]=q;
21         else{
22             nc(ml[x]+1,r),f[r]=f[q],f[p]=f[q]=r;
23             memcpy(tr[r],tr[q],sizeof(tr[r]));
24             while(x&&tr[x][w]==q)tr[x][w]=r,x=f[x];
25         }
26     }
27     void upright(int mx=0){
28         F(i,0,ed)d[i]=0;
29         F(i,1,ed)d[mx<ml[i]?mx=ml[i]:ml[i]]++;
30         F(i,1,mx)d[i]+=d[i-1];
31         F(i,1,ed)b[d[ml[i]]--]=i;
32         for(int i=ed;i;--i)cnt[f[b[i]]]+=cnt[b[i]];
33     }
34     void build(char *s){for(int i=1;s[i];i++)add(gid(s[i]));}
35 
36     long long sum[M];
37     void getsum(int op=0){
38         for(int i=ed;i;i--){
39             int x=b[i];sum[x]=op?cnt[x]:1;
40             F(j,0,tyn-1)sum[x]+=sum[tr[x][j]];
41         }
42     }
43     void print_min(long long k,int op=0,int rt=1)
44     {
45         if(rt!=1&&k<=(op?cnt[rt]:1))return;
46         if(rt!=1)k-=(op?cnt[rt]:1);
47         F(i,0,tyn-1)if(tr[rt][i])
48         {
49             if(k>sum[tr[rt][i]])k-=sum[tr[rt][i]];
50             else{
51                 printf("%c",i+‘a‘);
52                 print_min(k,op,tr[rt][i]);
53                 break;
54             }
55         }
56     }
57 }sam;
58 char s[N];
59 int a;
60 long long b;
61 
62 int main()
63 {
64     scanf("%s",s+1);
65     scanf("%d%lld",&a,&b);
66     sam.clear(),sam.build(s),sam.upright();
67     sam.getsum(a),sam.print_min(b,a);puts("");
68     return 0;
69 }