格雷码 CSP（NOIP？？）2019 洛谷 P5657

#include <bits/stdc++.h>
using namespace std;
#define ll unsigned long long

inline ll pow(ll x){
    ll a = 1, temp = 2;
    for(int i = 1;i <= x; i++){
        a *= temp;
    }
    return a;
}

ll a[100], cnt = 0;

void dfs(ll n, ll k){    
    if(n == 1){
        if(k == 1) a[++cnt] = 1;
        else a[++cnt] = 0;
        return ;
    }
    if(k >= (pow(n) / 2) ) 
        dfs(n - 1, (pow(n) - k - 1));
    else dfs(n - 1, k);
    if(k >= pow(n) / 2) a[++cnt] = 1;
    else a[++cnt] = 0;
    return ;
}

int main(){
//    freopen("hh.txt", "r", stdin);
    ll n, k;
    cin >> n >> k;
    dfs(n, k);
    for(int i = cnt;i > 0; i--)    printf("%d", a[i]);
    return 0;
}