[TJOI2015]弦论(后缀自动机)

/*
一道在树上乱搞的题目
建立出parent树来， 然后就能搞出每个节点往后能扩展出几个串， 至于位置不同算同一个的话就强制让right集合大小为1即可
然后在树上类比权值线段树找第k大26分统计一下即可 
*/
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
#include<iostream>
#define ll long long
#define mmp make_pair
#define M 1000100
using namespace std;
int read()
{
	int nm = 0, f = 1;
	char c = getchar();
	for(; !isdigit(c); c = getchar()) if(c == '-') f = -1;
	for(; isdigit(c); c = getchar()) nm = nm * 10 + c - '0';
	return nm * f;
}
int t, k;
char s[M];
int ch[M][26], sz[M], len[M], fa[M], tim[M], a[M], f[M], lst = 1, cnt = 1;
void insert(int c)
{
	int p = ++cnt, f = lst;
	lst = p;
	len[p] = len[f] + 1;
	sz[p] = 1;
	while(f && !ch[f][c]) ch[f][c] = p, f = fa[f];
	if(!f) fa[p] = 1;
	else
	{
		int q = ch[f][c];
		if(len[q] == len[f] + 1) fa[p] = q;
		else
		{
			int nq = ++cnt;
			memcpy(ch[nq], ch[q], sizeof(ch[q]));
			fa[nq] = fa[q];
			len[nq] = len[f] + 1;
			fa[q] = fa[p] = nq;
			while(f && ch[f][c] == q) ch[f][c] = nq, f = fa[f];
		}
	}
}
void query(int now, int k)
{
	if(k <= sz[now]) return;
	k -= sz[now];
	for(int i = 0; i < 26; i++)
	{
		if(f[ch[now][i]] < k) k -= f[ch[now][i]];
		else
		{
			putchar('a' + i);
			query(ch[now][i], k);
			break;
		}
	}
}
int main()
{
	scanf("%s", s + 1);
	int l = strlen(s + 1);
	for(int i = 1; i <= l; i++) insert(s[i] - 'a');
	for(int i = 1; i <= cnt; i++) tim[len[i]]++;
	for(int i = 1; i <= cnt; i++) tim[i] += tim[i - 1];
	for(int i = 1; i <= cnt; i++) a[tim[len[i]]--] = i;
	for(int i = cnt; i >= 1; i--) sz[fa[a[i]]] += sz[a[i]];
	t = read(), k = read();
	if(t == 0) for(int i = 1; i <= cnt; i++) f[i] = sz[i] = 1;
	else for(int i = 1; i <= cnt; i++) f[i] = sz[i];
	f[1] = sz[1] = 0;
	for(int i = cnt; i >= 1; i--)
	{
		for(int j = 0; j < 26; j++)
		{
			f[a[i]] += f[ch[a[i]][j]];
		}
	}
	if(k > f[1]) return 0 * puts("-1");
	else query(1, k);
	return 0;
}