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)

{// 下界約束

x[t]= centerx ;

Backtrack(t+1);}

Swap(r[t], r[j]);}

}

float Circle::Center( int t)

{// 計算當前所選擇圓的圓心橫坐標

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)

{// 計算當前圓排列的長度

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;

}