input
aa
2
output
a
input
abc
5
output
bc
input
abab
7
output
b
题意
给定s,输出其字典序第k小的子串
思路
首先将单个字符放入multiset中,之后每次向后扩展新的子串放入multiset(使用优先队列莫名其妙会TLE……)后在进行选择,直到找到第k大的子串
代码
#pragma GCC optimize(2)
#include<iostream>
#include<unordered_map>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<map>
#include<set>
#define Buff ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#define rush() int Case = 0; int T; cin >> T; while(T--)
#define rep(i, a, b) for(int i = a; i <= b; i ++)
#define per(i, a, b) for(int i = a; i >= b; i --)
#define reps(i, a, b) for(int i = a; b; i ++)
#define clc(a, b) memset(a, b, sizeof(a))
#define Buff ios::sync_with_stdio(false)
#define readl(a) scanf("%lld", &a)
#define readd(a) scanf("%lf", &a)
#define readc(a) scanf("%c", &a)
#define reads(a) scanf("%s", a)
#define read(a) scanf("%d", &a)
#define lowbit(n) (n&(-n))
#define pb push_back
#define sqr(x) x*x
#define lson rt<<1
#define rson rt<<1|1
#define ls lson, l, mid
#define rs rson, mid+1, r
#define y second
#define x first
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int>PII;
const int mod = 1e9+7;
const double eps = 1e-6;
const int N = 1e6+7;
string s, t;
struct node
{
string s;
int id;
bool operator<(node a)const
{
return s < a.s;
}
}res;
multiset<node> se;
int main()
{
int k, n;
cin >> s >> k;
n = s.size();
reps(i, 0, s[i])
{
res.s = s[i]; res.id = i+1;
se.insert(res);
}
int tot = 0;
while(se.size())
{
auto it = se.begin();
res = *it;
se.erase(it);
tot ++;
if(tot == k) break;
if(res.id < n)
{
t = res.s;
t += s[res.id];
se.insert({t, res.id+1});
}
}
if(tot == k) cout << res.s <<endl;
else puts("No such line.");
return 0;
}