Codeforces Round #428 (Div. 2) E. Mother of Dragons
2017-08-28 13:18
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题目大意
n个城堡间有些城堡有墙,将k点能量分给城堡,每个墙的防御值为u*v,求防御值最大是多少。(n<=40,k<=1000)
题解
分析一下(猜一下)结论知,平均分给最大团最大。求最大用类似A*的Bron-Kerbosch算法。证明:
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> using namespace std; int a[45][45]; int d[45],b[45]; int maxn,n; void dfs(int k,int r) { bool flag; if(r+n-k+1<=maxn) return; if(k==n+1) { if(r>maxn) maxn=r; return; } flag=1; if(d[k]<=maxn-1) flag=0; else { for(int i=1;i<=r;i++) { if(a[b[i]][k]==0) { flag=0; break; } } } if(flag) { b[r+1]=k; dfs(k+1,r+1); } dfs(k+1,r); } int main() { int k; double ans; cin>>n>>k; memset(d,0,sizeof(d)); for(int i=1;i<=n;i++) { for(int j=1;j<=n;j++) { scanf("%d",&a[i][j]); if(a[i][j]==1) d[i]++; } } maxn=1,dfs(1,0); ans=(maxn-1)*k*k*1.0/(2*maxn); printf("%.12lf",ans); }
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