Many Equal Substrings CF - 1029A （KMP）

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn = 4e5 + 10;
int n,k;
char s[maxn];
int l;
int nxt[maxn];
int ans[maxn];
void work() {
    for (int i = 2, j = 0; i <= l; i++) {
        while (j > 0 && s[i] != s[j + 1])
            j = nxt[j];
        if (s[i] == s[j + 1]) j++;
        nxt[i] = j;
    }
}



int main() {
    //freopen("in","r",stdin);
    scanf("%d %d",&n,&k);
   scanf("%s", s + 1);
   l = strlen(s + 1);
   work();
   printf("%s",s+1);
   k--;
   while(k--){
       for(int i = nxt[l] + 1;i <= l; i++)
           printf("%c",s[i]);
    }
    printf("\n");
    return 0;
}