扩展欧几里德算法

欧几里德的推广形式， 使其能计算出满足下面条件的整系数x,y:

d = gcd(a, b) = ax + by

void extend_Eulid(int a, int b){    if (b == 0) {        x = 1;        y = 0;        d = a;    }    else {        extend_Eulid(b, a%b);        int tmp = x;        x = y;        y = tmp - a/b*y;    }}