Codeforces 525E Anya and Cubes

http://codeforces.com/contest/525/problem/E

题意:

有n个方块，上面写着一些自然数，还有k个感叹号可用。k<=n 
你可以选任意个方块，然后选一些贴上感叹号使上面的数值变成阶乘，然后把方块上的值加起来会得到一个和。 
求和等于S的选择方法数。

思路:折半搜索，然后把所有状态按权值排序，然后统计

 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<iostream>
 #define ll long long
 struct node{
     ll v,st;
     int id,y;
 }b[],c[];
 int tot1,tot2;
 int n,K,flag,a[],d[];
 ll S,bin[],jc[],ans;
 bool cmp(node a,node b){
     return a.v<b.v;
 }
 ll read(){
     ll t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 int lowbit(int x){
     return (x)&(-x);
 }
 bool pd(ll st1,ll st2){
     int cnt=;
     while (st1){
         ll t=st1%;
         if (t==) cnt++;
         st1/=;
     }
     while (st2){
         ll t=st2%;
         if (t==) cnt++;
         st2/=;
     }
     return cnt<=K;
 }
 void dfs(int k,ll st,ll res,int cnt,int lim){
     if (k>lim){
         if (flag==){
             tot1++;
             b[tot1].v=res;
             b[tot1].st=st;
             b[tot1].id=;
             b[tot1].y=cnt;
         }else{
             tot2++;
             c[tot2].v=res;
             c[tot2].st=st;
             c[tot2].id=;
             c[tot2].y=cnt;
         }
         return;
     }
     dfs(k+,st+bin[k-]*,res,cnt,lim);
     dfs(k+,st+bin[k-]*,res+a[k],cnt,lim);
     if (a[k]<=&&res+jc[a[k]]<=S&&cnt+<=K)
     dfs(k+,st+bin[k-]*,res+jc[a[k]],cnt+,lim);
 }
 int num(ll x){
     int cnt=;
     while (x){
         ll t=x%;
         if (t==) cnt++;
         x/=;
     }
     return cnt;
 }
 void up(int x,int v){
     for (int i=x;i<=K;i++)
      d[i]+=v;
 }
 int ask(int x){
     return d[x];
 }
 int main(){
     n=read();K=read();S=read();
     bin[]=;
     for (int i=;i<=;i++)
      bin[i]=bin[i-]*;
     jc[]=;
     for (int i=;i<=;i++)
      jc[i]=jc[i-]*i;
     for (int i=;i<=n;i++)
       a[i]=read();
     flag=;
     dfs(,,,,(n+)>>);
     flag=;
     dfs(((n+)>>)+,,,,n);
     std::sort(b+,b++tot1,cmp);
     std::sort(c+,c++tot2,cmp);
     int j=tot2;
     for (int i=;i<=tot1&&j;){
         for (;j&&b[i].v+c[j].v>S;j--);
         if (b[i].v+c[j].v==S){
             for (int y=;y<=K;y++) d[y]=;
             for (;i<=tot1&&b[i].v+c[j].v==S;i++) d[b[i].y]++;
             for (int y=;y<=K;y++) d[y]+=d[y-];
             for (;j&&b[i-].v+c[j].v==S;j--) ans+=d[K-c[j].y];
         }else i++;
     }
     printf("%I64d\n",ans);
     return ;
 }