只有10分，只AC了两个点!!

#include <bits/stdc++.h>

using namespace std;

int main()
{
	int t;
	cin>>t;
    int n,a,d,sum;
	for (int i=1;i<=t;i++)
	{
		sum=0;
	    cin>>n>>a>>d;
	    if(d==1||a%2!=0&&d%2!=0||a%2==0&&d%2!=0)
	    {
	        cout<<"0"<<endl;
	        continue; 
	    }
	    if(a%2!=0&&d%2==0)
		{
			sum=(n/2+1)*n/2;
			if(n%2==0)
			{
				sum-=n/2;
			}
			cout<<sum<<endl;
			continue; 
		} 
		if(a%2==0&&d%2==0)
		{
			sum=(n/2+1)*n/2;
			if(n%2==0)
			{
				sum-=n/2;
			}
			cout<<sum<<endl;
			continue; 
		} 
		if(n==2)
		{
			cout<<"0"<<endl;
		} 
	}
	return 0;
}

推导了$80$分钟无果！！ 球球大佬解答！！！