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| #include <cstdio>
#include <bitset>
using namespace std;
template <class Type>
void read(Type &x)
{
char c;
bool flag = false;
while ((c = getchar()) < '0' || c > '9')
c == '-' && (flag = true);
x = c - '0';
while ((c = getchar()) >= '0' && c <= '9')
x = (x << 3) + (x << 1) + c - '0';
flag && (x = ~x + 1);
}
template <class Type>
void write(Type x)
{
x < 0 && (putchar('-'), x = ~x + 1);
x > 9 && (write(x / 10), 0);
putchar(x % 10 + '0');
}
const int N = 40;
bool vis[N];
int n, m, ans;
bitset<N> A[N];
void dfs (int x, int s)
{
if (s >= ans)
return;
if (!x)
return ans = s, void();
if (A[x][x])
{
bool v = A[x][0];
for (int i = x + 1; i <= n; i++)
A[x][i] && (v ^= vis[i]);
dfs(x - 1, s + v);
}
else
{
dfs(x - 1, s);
vis[x] = true;
dfs(x - 1, s + 1);
vis[x] = false;
}
}
void Gauss()
{
for (int k = 1; k <= n; k++)
{
int t = k;
while (t <= n && !A[t][k])
t++;
if (t > n)
continue;
swap(A[t], A[k]);
for (int i = 1; i <= n; i++)
i ^ k && A[i][k] && (A[i] ^= A[k], 0);
}
}
int main ()
{
read(n), read(m);
for (int a, b; m; m--)
{
read(a), read(b);
A[a][b] = A[b][a] = 1;
}
for (int i = 1; i <= n; i++)
{
A[i][i] = 1;
A[i][0] = 1;
}
Gauss();
ans = n;
dfs(n, 0);
write(ans);
return 0;
}
|