由两个有限项的等差数列B, C, 求有多少个有限项的等差数列A，满足C是A, B的所有公共项，若有无穷个A满足条件，输出-1

题目

思路：

#include 
using namespace std;
#define int long long
#define pb push_back
const int maxn = 1e6 + 5, inf = 1e9 + 5, maxm = 4e4 + 5, mod = 1e9 + 7, N = 1e6;
// int a[maxn], b[maxn];
int n, m;
string s;

int qpow(int a, int b){
    int res = 1;
    while(b){
        if(b & 1) res = res * a % mod;
        a = a * a % mod;
        b >>= 1;
    }
    return res;
}

int __lcm(int a, int b){
    int g = __gcd(a, b);
    return a * b / g;
}

void solve()
{
    int res = 0;
    int a, b