用一个大一点的数组就过了

C++ 代码

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
const int N = 5000005;
int n, m;
struct sum
{
    int c,d;
    bool operator< (const sum& t)const
    {
        if (c != t.c) return c < t.c;
        return d < t.d;
    }
}sum[N];
int main()
{
    cin >> n;
    for (int c = 0; c * c <= n; c++)
        for (int d = c; c * c + d * d <= n; d++)
        {
            if (sum[c * c + d * d].c==sum[c * c + d * d].d&&sum[c * c + d * d].c==0)
            {
                sum[c * c + d * d] = {c,d};
            }
        }

    for (int a = 0; a * a <= n; a++)
    {
        for (int b = 0; a * a + b * b <= n; b++)
        {
            int t = n - a * a - b * b;
            if (pow(sum[t].c,2)+pow(sum[t].d,2)==t)
            {
                printf("%d %d %d %d\n", a, b, sum[t].c, sum[t].d);
                return 0;
            }
        }
    }
    return 0;
}