1.1最大公约数与最小公倍数
1.算法1: 欧几里德算法求a,b的最大公约数
function gcd(a,b:longint):longint;
begin
if b=0 then gcdd:=a
else gcd:=gcd(b,a mod b);
end;
2.算法2:最小公倍数acm=a*b div gcd(a,b);
3.算法3:扩展的欧几里德算法,求出gcd(a,b)和满足gcd(a,b)=ax+by的整数x和y
function exgcd(a,b:longint;var x,y:longint):longint;
var
t:longint;
begin
if b=0 then
begin
result:=a;
x:=1;
y:=0;
end
else
begin
result:=exgcd(b,a mod b,x,y);
t:=x;
x:=y;
y:=t-(a div b)*y;
end;
end;
（理论依据：gcd(a,b)=ax+by=bx1+(a mod b)y1=bx1+(a-(a div b)*b)y1=ay1+b(x1-(a div b)*y1))
