python/TangDou/CSP-J/J2-2021/AcWing1221_ErFen_2.cpp

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

const int N = 5e6 + 10;

struct Node {
    int c, d, sum;
    bool operator<(const Node &t) const {
        if (sum != t.sum) return sum < t.sum;
        if (c != t.c) return c < t.c;
        return d < t.d;
    }
} f[N];

int n;
int idx;

int main() {
    scanf("%d", &n);

    // C预处理出 c^2+d^2
    for (int c = 0; c * c <= n; c++)
        for (int d = c; c * c + d * d <= n; d++)
            f[idx++] = {c, d, c * c + d * d};

    //结构体排序
    sort(f, f + idx);

    //枚举a^2+b^2
    for (int a = 0; a * a <= n; a++) {
        for (int b = a; a * a + b * b <= n; b++) {
            int t = n - a * a - b * b;

            //手写二分模板,左闭右开
            // STL二分缺点:
            // 1、常数较大,速度慢
            // 2、对于结构体二分，需要构造空的Struct,还需要有一些玄学的赋零操作，不推荐
            //结论：全面采用手写二分办法，忘记STL的二分写法
            int l = 0, r = idx;
            while (l < r) {
                int mid = (l + r) >> 1;
                if (f[mid].sum >= t)
                    r = mid;
                else
                    l = mid + 1;
            }
            if (f[l].sum == t) {
                cout << a << ' ' << b << ' ' << f[l].c << ' ' << f[l].d << ' ' << endl;
                exit(0);
            }
        }
    }
    return 0;
}