算法1

时间复杂度

$O(sqrt^3(n))$

C++ 代码

#include <iostream>
#include <cmath>
using namespace std;
int main(){
    int n;
    cin >> n;
    int l = 0, r = sqrt(n);
    for(int i = 0;i <= r;i++){
        for(int j =i;j <= r;j++){
            int low = j, high = sqrt(n);
            int temp = i * i + j * j;
            while (low < high){ // 双指针
                if(temp + low * low + high * high > n) high--;
                else if (temp + low * low + high * high < n) low++;
                else {cout << i << " " << j << " " << low <<  " " << high << endl;
                return  0;
                }
            }

        }
    }
}