uva 10012

题目意思：  给定m个圆的半径，现在要求找到一个矩形使得每一个球都以地面相切，要求输出最小的矩阵的长度

 1 #include <iostream>

 2 #include <algorithm>

 3 #include <cstring>

 4 #include <cstdlib>

 5 #include <cstdio>

 6 #include <cmath>

 7 using namespace std;

 8 int num;

 9 bool vis[10];

10 double a[8], c[8], l[8], _max;

11 double sqr(double r)

12 {

13     return r*r;

14 }

15 

16 void dfs(int cnt, double len)

17 {

18     if(len > _max)

19         return ;

20     if(cnt == num)

21     {

22         double ll = c[0];

23         len += c[cnt - 1];

24         for(int i = 0; i < num - 1; i++)

25             if(l[i] + c[i] > len)

26                 len = l[i] + c[i];

27         for(int i = 1; i < num; i++)

28             if(c[i] - l[i] > ll)

29                 ll = c[i] - l[i];

30         len += ll;

31         if(len < _max)

32             _max = len;

33         return ;

34     }

35     for(int i = 0; i < num; i++)

36     {

37         if(vis[i]) continue;

38         vis[i] = true;

39         c[cnt] = a[i];

40         l[cnt] = c[cnt];

41         for(int j = cnt - 1; j >= 0; j--)

42         {

43             double dis = l[j] + sqrt(sqr(c[j]+c[cnt])-sqr(c[j]-c[cnt]));

44             if(dis > l[cnt])

45                 l[cnt] = dis;

46         }

47         dfs(cnt + 1, l[cnt]);

48         vis[i] = false;

49     }

50 }

51 int main()

52 {

53     int n;

54     scanf("%d", &n);

55     memset(vis, 0, sizeof(vis));

56     while(n--)

57     {

58         _max = 0x7FFFFFFF;

59         scanf("%d", &num);

60         for(int i = 0; i < num; i++)

61             scanf("%lf", &a[i]);

62         for(int i = 0; i < num; i++)

63         {

64             vis[i] = true;

65             l[0] = 0;

66             c[0] = a[i];

67             dfs(1, 0);

68             vis[i] = false;

69         }

70         printf("%.3lf\n", _max);

71     }

72     return 0;

73 }

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