P1284 三角形牧场

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 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<queue>
 6 #include<algorithm>
 7 #include<map>
 8 #define lli long long int 
 9 using namespace std;
10 const int MAXN=10000001;
11 void read(int &n)
12 {
13     char c='+';int x=0;bool flag=0;
14     while(c<'0'||c>'9')
15     {c=getchar();if(c=='-')flag=1;}
16     while(c>='0'&&c<='9')
17     {x=x*10+(c-48);c=getchar();}
18     flag==1?n=-x:n=x;
19 }
20 int n;
21 int fi,se;
22 int vis[MAXN];
23 int sum=0;
24 int a[MAXN];
25 int happen[MAXN];
26 double ans=-1;
27 map<string,bool>mp;
28 double calc(double yi,double er,double san)
29 {
30     if(min(min(yi,er),min(er,san))+min(min(yi,er),min(er,san))>max(max(yi,er),max(er,san)))
31     {
32         double p=(yi+er+san)/2;
33         return sqrt(p*(p-yi)*(p-er)*(p-san));    
34     }
35     else
36     return -1;
37 }
38 int comp(const int a,const int b)
39 {
40     return a<b;
41 }
42 void dfs(int yi,int er,int san)
43 {
44     if(happen[yi*1500+er*150+san])
45         return ;
46     happen[yi*1500+er*150+san]=1;
47     if(yi+er+san==sum&&yi!=0&&er!=0&&san!=0)
48     {
49         double hh=calc(yi,er,san);
50         if(hh>ans)
51         ans=calc(yi,er,san);
52     }
53         
54     for(int i=1;i<=n;i++)
55     {
56         if(vis[i]==0)
57         {
58             vis[i]=1;
59             dfs(yi+a[i],er,sum-(yi+a[i]+er));
60             dfs(yi,er+a[i],sum-(yi+er+a[i]));
61             vis[i]=0;
62             dfs(yi,er,sum-(yi+er));
63         }
64     }
65 }
66 int main()
67 {
68     
69     read(n);
70     for(int i=1;i<=n;i++)
71     {
72         read(a[i]); sum+=a[i];    
73     }
74     sort(a+1,a+n+1,comp);// 排序是为了方便调试 
75     dfs(0,0,0);
76     if(ans==-1)
77     { printf("-1"); return 0;}
78     ans=ans*100.0;
79     printf("%d",(int)ans);
80     return 0;
81 }