结构体重载符号固定格式

bool operator< (const struct &a)const
{
    return c<a.c
}

#include<bits/stdc++.h>
using namespace std;
const int N = 1e7;
int n,m;
struct Sum
{
    int s,c,d;
    bool operator< (const Sum &a)const
    {
        if(s != a.s)return s<a.s;
        if(c != a.c)return c<a.c;
        return d<a.d;
    }

}sum[N];

int main()
{
    cin>>n;
    for(int c = 0;c*c<=n;c++)
        for(int d = c;d*d+c*c<=n;d++)//如果没有c*c+d*d，只考虑d*d可能会导致d不合法
            sum[m++] = {c*c+d*d,c,d};

    sort(sum,sum+m);

    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;
            int l = 0,r = m-1;     //枚举的是sum的s sum的大小为m
            while(l<r)
            {
                int mid = (l+r)>>1;
                if(sum[mid].s >= t) r = mid;
                else l = mid+1;
            }
            if(sum[l].s ==t)
            {
                printf("%d %d %d %d",a,b,sum[l].c,sum[l].d);
                return 0;
            }
        }
    return 0;
}