扩展欧几里得算法

exgcd(a,b,x,y)
{
     if(b==0)  x=1,y=0;
     else
           exgcd(a,a%b,y,x-(a/b)*y;    
}        

ax1+by1=c;
ax2+by2=c;
a(x1-x2)+b(y1-y2)=0;
x=x1-x2;
y=y1-y2;
g=gcd(a,b);
a=a0*g;
b=b0*g;
a0*g*x+b0*g*y=0;
x=-b0,y=a0;
x=b0,y=-a0;