題目連結

Description

You are given a string $t$ consisting of $n$ lowercase Latin letters and an integer number $k$.

Let’s define a substring of some string $s$ with indices from $l$ to $r$ as $s[l…r]$.

Your task is to construct such string $s$ of minimum possible length that there are exactly $k$

It is guaranteed that the answer is always unique.

Input

The first line of the input contains two integers $n$

The second line of the input contains the string $t$ consisting of exactly $n$ lowercase Latin letters.

Output

Print such string $s$ of minimum possible length that there are exactly $k$ substrings of $s$

It is guaranteed that the answer is always unique.

Examples

jnput

3 4 aba

Output

ababababa

Input

3 2 cat

Output

catcat

類似 $KMP$ 演算法，我們求出一個最長的相同字首字尾長度，即 $next$ 陣列，然後輸出 $k-1$ 個 $S[i],i∈\big[0,s.size()-next[n-1]\big]$，最後再輸出 $S$。

#include<cstdio>
#include<iostream>
using namespace std;
int nx[110];
int main()
{
	//freopen("in.txt","r",stdin);
	int n,k;
	string s;
	cin>>n>>k>>s;
	for(int i=1,j=0;i<s.size();i++)
	{
		while(j&&s[i]!=s[j])j=nx[j-1];
		if(s[i]==s[j])j++;
		nx[i]=j;
	}
	int len=s.size()-nx[n-1];
	for(int i=1;i<k;i++)
	    cout<<s.substr(0,len);
	cout<<s;
	return 0;
}

總結

字串演算法沒怎麼寫過題，很生疏。