[数位DP] BZOJ 3209 花神的数论题

求出有i个1的数有多少

然后快速幂

#include<cstdio>#include<cstdlib>#include<algorithm>using namespace std;  typedef long long ll;    const int N=100005;  const int M=255;  const int P=10000007;    ll a[N],len,n;  ll C[M][M];    inline void Pre(){   for(int i=0;i<60;i++){  C[i][0]=1;  for(int j=1;j<=i;j++)C[i][j]=C[i-1][j]+C[i-1][j-1];}  }    inline ll Solve(ll k){  ll ans=0;  for(ll i=len;i>=1;i--){  if(a[i])ans+=C[i-1][k],k--;if(k<0) return ans;  }return ans;  }  inline ll Pow(ll a,ll b){ll ret=1; a%=P;for (;b;b>>=1,a=a*a%P)if (b&1)ret=ret*a%P;return ret;}  int main()  {Pre();  scanf("%lld",&n);n++; len=0;while (n) a[++len]=n%2,n>>=1;ll ans=1;  for(int i=1;i<=len;i++)  ans=ans*Pow(i,Solve(i))%P;  printf("%lld\n",ans);return 0;  }