扩展欧几里德算法

poj.1061.青蛙的约会

int gcd_ex(int a,int b,int &x,int &y){
    if(b == 0){
        x = 1;
        y = 0;
        return a;
    }
    else{
        int gcd = gcd_ex(b,a%b,x,y);
        int tempx = x;
        x = y;
        y = tempx - (a/b) * y;
        return gcd;
    }
}

求二元一次方程的整数解