只测试了几个数据

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

const int N = 2e5 + 10;

int n;
string str;
int ans;

int main()
{
    cin >> n;
    cin >> str;
    str += str;
    str = " " + str;

    int i = 1, j = 2, k;
    while(i <= n && j <= n){
        // 看到哪不匹配
        for(k = 0; k < n && str[i + k] == str[j + k]; ) k ++;

        if(k == n) break;

        if(str[i + k] > str[j + k]){
            i = i + k + 1;
            if(i == j) i ++;
        }
        else{
            j = j + k + 1;
            if(i == j) j ++;
        }
    }

    ans = min(i, j);

    for(int i = 0; i < n; i ++)
        cout << str[ans + i];
    puts("");

    return 0;
}