1130: [POI2008]POD Subdivision of Kingdom

1130: [POI2008]POD Subdivision of Kingdom

https://lydsy.com/JudgeOnline/problem.php?id=1130

分析：

　　有效状态为$C_{26}^{13}$，所以直接搜索就好了。

代码：

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<iostream>
 #include<cmath>
 #include<cctype>
 #include<set>
 #include<queue>
 #include<vector>
 #include<map>
 #include<bitset>
 using namespace std;
 typedef long long LL;

 inline int read() {
     int x=,f=;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-;
     for(;isdigit(ch);ch=getchar())x=x*+ch-'';return x*f;
 }

 const int N = ;

 int e[], num[N];
 int All, n, mn = 1e9, ans;

 int Calc(int x) {
     return num[x >> ] + num[x & (( << ) - )];
 }
 void dfs(int x,int last,int sta,int cnt) { // 当前已经有多少点，上一个点，状态，边数
     if (x == n / ) {
         if (cnt < mn) mn = cnt, ans = sta;
         return ;
     }
     for (int i = last + ; i < n; ++i) {
         if ((sta >> i) & ) continue;
         dfs(x + , i, sta | ( << i), cnt - Calc(sta & e[i]) + Calc((All ^ sta) & e[i])); // ^和&的优先级！！
     }
 }
 int main() {
     n = read();int m = read();
     All = ( << n) - ;
     for (int i = ; i <= m; ++i) {
         int u = read() - , v = read() - ;
         e[u] |= ( << v), e[v] |= ( << u);
     }
     for (int i = ; i < ( << ); ++i) num[i] = num[i >> ] + (i & );
     dfs(, -, , );
     if (!(ans & )) ans = (( << n) - ) ^ ans;
     for (int i = ; i < n; ++i)
         if ((ans >> i) & ) cout << i +  << " ";
     return ;
 }