Codeforces Beta Round #94 (Div. 1 Only)B. String sam

题意:给你一个字符串,找第k大的子字符串.(考虑相同的字符串)

题解:建sam,先预处理出每个节点的出现次数,然后处理出每个节点下面的出现次数,然后在dfs时判断一下往哪边走即可,注意一下num会爆int

//#pragma GCC optimize(2)
//#pragma GCC optimize(3)
//#pragma GCC optimize(4)
//#pragma GCC optimize("unroll-loops")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include<bits/stdc++.h>
#define fi first
#define se second
#define db double
#define mp make_pair
#define pb push_back
#define pi acos(-1.0)
#define ll long long
#define vi vector<int>
#define mod 998244353
#define ld long double
//#define C 0.5772156649
//#define ls l,m,rt<<1
//#define rs m+1,r,rt<<1|1
#define pll pair<ll,ll>
#define pil pair<int,ll>
#define pli pair<ll,int>
#define pii pair<int,int>
#define ull unsigned long long
//#define base 1000000000000000000
#define fin freopen("a.txt","r",stdin)
#define fout freopen("a.txt","w",stdout)
#define fio ios::sync_with_stdio(false);cin.tie(0)
inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
inline void sub(ll &a,ll b){a-=b;if(a<0)a+=mod;}
inline void add(ll &a,ll b){a+=b;if(a>=mod)a-=mod;}
template<typename T>inline T const& MAX(T const &a,T const &b){return a>b?a:b;}
template<typename T>inline T const& MIN(T const &a,T const &b){return a<b?a:b;}
inline ll qp(ll a,ll b){ll ans=1;while(b){if(b&1)ans=ans*a%mod;a=a*a%mod,b>>=1;}return ans;}
inline ll qp(ll a,ll b,ll c){ll ans=1;while(b){if(b&1)ans=ans*a%c;a=a*a%c,b>>=1;}return ans;}

using namespace std;

const ull ba=233;
const db eps=1e-7;
const ll INF=0x3f3f3f3f3f3f3f3f;
const int N=100000+10,maxn=100000+10,inf=0x3f3f3f3f;

struct SAM{
    int last,cnt;
    int ch[N<<1][26],fa[N<<1],l[N<<1];
    ll sz[N<<1],num[N<<1];
    int a[N<<1],c[N<<1],vis[N<<1];
    void ins(int c){
        int p=last,np=++cnt;last=np;l[np]=l[p]+1;
        for(;p&&!ch[p][c];p=fa[p])ch[p][c]=np;
        if(!p)fa[np]=1;
        else
        {
            int q=ch[p][c];
            if(l[p]+1==l[q])fa[np]=q;
            else
            {
                int nq=++cnt;l[nq]=l[p]+1;
                memcpy(ch[nq],ch[q],sizeof(ch[q]));
                fa[nq]=fa[q];fa[q]=fa[np]=nq;
                for(;ch[p][c]==q;p=fa[p])ch[p][c]=nq;
            }
        }
        sz[np]=1;
    }
    void topo()
    {
        for(int i=1;i<=cnt;i++)c[l[i]]++;
        for(int i=1;i<=cnt;i++)c[i]+=c[i-1];
        for(int i=1;i<=cnt;i++)a[c[l[i]]--]=i;
    }
    void build(char *s){
        int len=strlen(s);
        last=cnt=1;
        for(int i=0;i<len;i++)ins(s[i]-'a');
        topo();
        for(int i=cnt;i;i--)sz[fa[a[i]]]+=sz[a[i]];
        sz[1]=0;
        dfs(1);
//        for(int i=1;i<=cnt;i++)
//        {
//            printf("%d %d ++",i,num[i]);
//            for(int j=0;j<26;j++)if(ch[i][j])printf("%d ",ch[i][j]);
//            puts("");
//        }
    }
    void dfs(int u)
    {
        vis[u]=1;
        num[u]=sz[u];
        for(int i=0;i<26;i++)if(ch[u][i])
        {
            if(!vis[ch[u][i]])dfs(ch[u][i]);
            num[u]+=num[ch[u][i]];
        }
    }
    void cal(int u,int k)
    {
        if(k<=0)return ;
        for(int i=0;i<26;i++)if(ch[u][i])
        {
            if(num[ch[u][i]]>=k)
            {
                printf("%c",i+'a');
//                printf("%d %d %d %c %d\n",u,ch[u][i],num[ch[u][i]],i+'a',k);
                cal(ch[u][i],k-sz[ch[u][i]]);
                return ;
            }
            else k-=num[ch[u][i]];
        }
    }
}sam;
char s[N];
int main()
{
    int k;
    scanf("%s%d",s,&k);
    sam.build(s);
    if(sam.num[1]<k)puts("No such line.");
    else sam.cal(1,k);
    return 0;
}
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