bzoj1224

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/syh0313/article/details/87970827

这题卡了我蛮久的qwq

其实就是一个暴力+前缀和剪枝

/**************************************************************

    Problem: 1224

    User: syh0313

    Language: C++

    Result: Accepted

    Time:6372 ms

    Memory:1288 kb

****************************************************************/

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cmath>

using namespace std;

const double eps=1e-10;

int n,m,ans;

double a,b,num,sum[60];

void dfs(int x,int cnt,double now)

{

    if (num-(now+sum[x+n-cnt-1]-sum[x-1])>eps) return;

    if (now+sum[m]-sum[m-(n-cnt)]-num>eps) return;

    if (abs(now-num)<eps) {ans++; return;}  

    if (cnt==n && abs(now-num)<eps) {ans++; return;}

    if (x>m) return;

    dfs(x+1,cnt+1,now+1.0/(double)x);

    dfs(x+1,cnt,now);

}

int main()

{

    scanf("%d%d%lf%lf",&n,&m,&a,&b); num=a/b;

    for (int i=1;i<=m;i++) sum[i]=sum[i-1]+1.0/(double)i;

    dfs(1,0,0.0);

    printf("%d\n",ans);

return 0;

}