void Circle::Backtrack( int t)
{
if (t>n) Compute();
else
for ( int j = t; j <= n; j++) {
Swap(r[t], r[j]);
float centerx =Center(t);
if ( centerx+r [t]+r[1]<min)
{// 下界约束
x[t]= centerx ;
Backtrack(t+1);}
Swap(r[t], r[j]);}
}
float Circle::Center( int t)
{// 计算当前所选择圆的圆心横坐标
float temp=0;
for ( int j=1;j< t;j ++) {
float valuex =x[j]+2.0* sqrt (r[t]*r[j]);
if ( valuex >temp) temp= valuex ;
}
return temp;
}
void Circle::Compute(void)
{// 计算当前圆排列的长度
float low=0,
high=0;
for ( int i =1;i<= n;i ++) {
if (x[ i ]-r[ i ]<low) low=x[ i ]-r[ i ];
if (x[ i ]+r[ i ]>high) high=x[ i ]+r[ i ];
}
if (high-low<min) min=high-low;
}
