秘密代码题解

#include <bits/stdc++.h>
using namespace std;
char s[40];
long long len;
void dfs(long long n,int h) {
    if (h == 0){
        cout << s[n];
        return;
    }
    long long tem = len * (1ll << (h - 1));
    if(tem >= n){
        dfs(n,h - 1);
    }else{
        if(n - tem == 1) dfs(tem,h - 1);
        else dfs(n - tem - 1,h - 1);
    }
}
int main(){
    cin >> s + 1;
    len = strlen(s + 1);
    long long n;
    cin >> n;
    for (int i = 0;;i ++) {
        if (len * (1ll << i) >= n){
            dfs(n,i);
            break;
        }
    }
    return 0;
}