题目来源：

​​https://ac.nowcoder.com/acm/contest/890/E​​

题意：

根据递归定义的希尔伯特曲线，给定n个该曲线上的坐标，按顺序输出

思路：

对每个点递归计算它的权值。根据当前层的坐标是x，y，讨论出上层的坐标，递归计算即可

代码：

#include<bits/stdc++.h>
using namespace std;

#define
#define
const int N=1e6+5;
int n,k;

struct node {
    int x, y;
    ll value;

    bool operator<(const node &b) const {
        return value < b.value;
    }
}p[N];

ll dfs(int x,int y,int k) {
    if (k == 0)
        return 0;
    ll kk = (1ll << k);
    ll value = kk * kk;
    if (x <= kk / 2 && y <= kk / 2)
        return dfs(y, x, k - 1);
    else if (x > kk / 2 && y <= kk / 2)
        return dfs(x - kk / 2, y, k - 1) + value;
    else if (x > kk / 2 && y > kk / 2)
        return dfs(x - kk / 2, y - kk / 2, k - 1) + value * 2;
    else if (x <= kk / 2 && y > kk / 2)
        return dfs(kk - y + 1, kk / 2 - x + 1, k - 1) + value * 3;
}

int main() {
    IOS;
    cin >> n >> k;
    for (int i = 1; i <= n; ++i) {
        cin >> p[i].x >> p[i].y;
        p[i].value = dfs(p[i].x, p[i].y, k);
    }
    sort(p + 1, p + 1 + n);
    for (int i = 1; i <= n; ++i)cout << p[i].x << " " << p[i].y << "\n";
    return 0;
}