ACM模版

GCD最大公约数

int gcd(int x, int y)
{
    if (!x || !y)
    {
        return x > y ? x : y;
    }

    for (int t; t = x % y, t; x = y, y = t) ;

    return y;
}

扩展GCD

/* * 求x，y使得gcd(a, b) = a * x + b * y; */
int extgcd(int a, int b, int &x, int &y)
{
    if (b == 0)
    {
        x = 1;
        y = 0;
        return a;
    }

    int d = extgcd(b, a % b, x, y);
    int t = x;
    x = y;
    y = t - a / b * y;

    return d;
}