是輾轉(zhuǎn)法
代碼：
long gcd(long x,long y)//最大公約數(shù)
{ // get the greatest common divisor of two integer(GCD)
long t;
if (x==0||y==0)
return 0;
if (x < 0)
x = -x;
if (y < 0)
y = -y;
if (x < y)
{
t = x;
x = y;
y = t;
}
while((t = x%y)!=0)
{
x = y;
y = t;
}
return y;
}
inline long lcm(long x,long y)//最小共倍數(shù)
{ // get the least common multiple of two integer(LCM)
return (x / gcd(x,y) * y);
}