Timer Switch

/*
    Task    : KMP
    Author  : Phumipat C. [MAGCARI]
    Language: C++
    Created : 01 February 2023 [20:10]
*/
#include<bits/stdc++.h>
using namespace std;
char a[10000010],b[5000010];
int kmp[5000010];
int main(){
    int lenb;
    scanf("%d %s",&lenb,b+1);
    for(int i=1;i<=lenb;i++)
        a[i] = a[lenb+i] = b[i];
    int lena = 2*lenb;
    // preprocess
    int j=0;
    for(int i=2;i<=lenb;i++){
        while(j>0 && b[j+1] != b[i])    j=kmp[j];
        if(b[j+1] == b[i])  j++;
        kmp[i]=j;
    }

    // search
    j=0;
    for(int i=2;i<=lena;i++){
        while(j>0 && b[j+1] != a[i])    j=kmp[j];
        if(b[j+1] == a[i])  j++;
        if(j == lenb){
            printf("%d\n",i-lenb);
            return 0;
        }
    }
    return 0;
}