最近点对模板：

             1 #include                   2 #include                     3 #include                       4 using namespace std;   5 const int MAXN = 100005;   6 struct POINT   7 {   8     double x, y;   9     int index;  10     void input()  11     {  12         scanf("%lf %lf", &x, &y);  13     }  14 }X[MAXN], Y[MAXN];  15 bool cmpx(const POINT &a, const POINT &b)  16 {  17     return a.x < b.x;  18 }  19 bool cmpy(const POINT &a, const POINT &b)  20 {  21     return a.y < b.y;  22 }  23 double dis(const POINT &a, const POINT &b)  24 {  25     return sqrt((a.x-b.x) * (a.x-b.x) + (a.y-b.y) * (a.y-b.y));  26 }  27 double min_dis(int a, int b, POINT *Y)  28 {  29     double ans = 1e8;  30     if (b-a <= 2)  31     {  32         for (int i = a; i < b; ++i)  33         {  34             for (int j = i+1; j <= b; ++j)  35             {  36                 double temp = dis(X[i], X[j]);  37                 if (ans > temp)  38                     ans = temp;  39             }  40         }  41         return ans;  42     }  43     int mid = (a+b) / 2;  44     POINT *Yl = new POINT[mid-a+1];  45     POINT *Yr = new POINT[b-mid];  46     int i, j, k, ind;  47     for (i = 0, j = 0, k = 0; i <= b-a; ++i)  48     {  49         if (Y[i].index <= mid) Yl[j++] = Y[i];  50         else Yr[k++] = Y[i];  51     }  52     double left_min = min_dis(a, mid, Yl);  53     double right_min = min_dis(mid+1, b, Yr);  54     ans = min(left_min, right_min);  55     double line = X[mid].x;  56     for (i = 0, ind = 0; i <= b-a; ++i)  57     {  58         if (fabs(Y[i].x - line) < ans)  59             Y[ind++] = Y[i];  60     }  61     for (i = 0; i < ind - 1; ++i)  62     {  63         for (j = i+1; j <= i+7 && j < ind; ++j)  64         {  65             double temp = dis(Y[i], Y[j]);  66             if (ans > temp)  67                 ans = temp;  68         }  69     }  70     delete []Yl;  71     delete []Yr;  72     return ans;  73 }  74 int main()  75 {  76     int n, i;  77     while (scanf("%d", &n), n)  78     {  79         for (i = 0; i < n; ++i)  80             X[i].input();  81         sort(X, X+n, cmpx);  82         for (i = 0; i < n; ++i)  83             X[i].index = i;  84         memcpy(Y, X, n * sizeof(POINT));  85         sort(Y, Y+n, cmpy);  86         printf("%.2lf\n", min_dis(0, n-1, Y) / 2);                   87     }  88     return 0;  89 }                               最后输出半径，要除以2.