洛谷P2236 HNOI2002 彩票 [暴搜]

　　题目传送门

彩票

 

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　　分析：

　　虽然题目标签上标的是Splay，但我一个蒟蒻至今也沒掌握平衡树，所以就索性一个暴搜，加一点剪枝就水过去了～

　　代码：

　　

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<iostream>
using namespace std;
const double eps=1e-10;
int n,m,X,Y,ans;
double com;
bool vis[51];
inline int read()
{
  char ch=getchar();int num=0;
  while(ch<'0'||ch>'9')
    ch=getchar();
  while(ch>='0'&&ch<='9'){
    num=num*10+ch-'0';
    ch=getchar();}
  return num;
}
inline double Fabs(double ka)
{return ka>0?ka:-ka;}
inline void dfs(int x,double num,int last)
{
  if(num-com>eps)return;
  if(num+(double)(n-x+1)*1.0/(double)(last+1)+eps<com)return;
  if(num+(double)(n-x+1)*1.0/(double)m>eps+com)return;
  if(x==n+1){
    if(Fabs(num-com)<=eps)ans++;
    return;}
  for(int i=last+1;i<=m;i++)
    if(!vis[i]){
      vis[i]=true;
      dfs(x+1,num+1.0/(double)i,i);
      vis[i]=false;
    }
  return;
}
int main()
{
  n=read();m=read();X=read();Y=read();
  com=(double)X/(double)Y;
  dfs(1,0,0);
  printf("%d",ans);
  return 0;
}