BZOJ1087: [SCOI2005]互不侵犯King(状压DP)

// luogu-judger-enable-o2
// luogu-judger-enable-o2
#include<cstdio>
#define int long long 
using namespace std;
const int MAXN = 10;
//#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<22,stdin),p1==p2)?EOF:*p1++)
char buf[1<<22],*p1=buf,*p2=buf;
inline int read() {
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}
    return x*f;
}
int f[MAXN][1<<MAXN][MAXN*MAXN];
int N, K;
int times[1<<MAXN],can[1<<MAXN];
int calc(int x) {
    int num = 0;
    for(int i = 0;i < N; i++)
        if( x & (1 << i) ) 
            num++;
    return num;
}
main() {
    #ifdef WIN32
    freopen("a.in","r",stdin);
    #endif
    //printf("%d %d %d\n",0<<1,0>>1,0);
    N = read(), K = read();
    int Max = (1 << N) - 1;
    for(int i = 0;i < Max; i++)
        times[i] = calc(i),
        can[i] = (i & (i>>1)) == 0 ? 1 : 0;
    f[0][0][0] = 1;
    for(int i = 1;i <= N; i++)
      for(int j = 0;j < Max; j++)
        if(can[j])
          for(int k = 0;k < Max; k++)
            if(((j & k) == 0) && ((j & (k << 1)) == 0) && ((j & (k >> 1)) == 0))
              for(int l = times[j]; l <= K; l++)
                f[i][j][l] += f[i-1][k][l - times[j]];
    int ans = 0;
    for(int i = 0;i <= Max; i++)
        ans += f[N][i][K];
    printf("%lld", ans);
    return 0;
}