AtCoder - 4130 K-th Substring

Problem Statement

You are given a string s. Among the different substrings of s, print the K-th lexicographically smallest one.

A substring of s is a string obtained by taking out a non-empty contiguous part in s. For example, if s = ababc, a, bab and ababc are substrings of s, while ac, z and an empty string are not. Also, we say that substrings are different when they are different as strings.

Let X=x₁x₂…x_n and Y=y₁y₂…y_m be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or x_j>y_j where j is the smallest integer such that x_j≠y_j.

Constraints

• 1 ≤ |s| ≤ 5000
• s consists of lowercase English letters.
• 1 ≤ K ≤ 5
• s has at least K different substrings.

Partial Score

• 200 points will be awarded as a partial score for passing the test set satisfying |s| ≤ 50.

Input

Input is given from Standard Input in the following format:

s
K

Output

Print the K-th lexicographically smallest substring of K.

Sample Input 1

aba
4

Sample Output 1

b

s has five substrings: a, b, ab, ba and aba. Among them, we should print the fourth smallest one, b. Note that we do not count a twice.

Sample Input 2

atcoderandatcodeer
5

Sample Output 2

andat

Sample Input 3

z
1

Sample Output 3

z

    一看这种题第一反应：裸上SAM啊！
    但是一看数据范围：艹这是连SAM都不用的傻逼题了。
因为字典序第K小肯定不会超过K位，所以直接暴力+去重就可以做了QWQ

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn=5005;
string ch[maxn*6];
char s[maxn];
int n,k,cnt;
int main(){
	scanf("%s%d",s,&k),n=strlen(s);
	for(int i=0,T;i<n;i++){
		ch[++cnt]=s[i];
		T=min(k,n-i);
		for(int j=1;j<T;j++,cnt++) ch[cnt+1]=ch[cnt]+s[i+j];
	}

	sort(ch+1,ch+cnt+1);
	unique(ch+1,ch+cnt+1);
	cout<<ch[k]<<endl;
	return 0;
}