hdu 4803 贪心/思维题

http://acm.hdu.edu.cn/showproblem.php?pid=4803

话说C++还卡精度么？  G++  AC  C++ WA

我自己的贪心策略错了 -- 就是尽量下键，然后上键，最后下键补全，可是例子都过不了.....

题解參考http://www.cnblogs.com/xuesu/p/3967704.html

http://www.cnblogs.com/Canon-CSU/p/3451784.html

http://blog.csdn.net/keshuai19940722/article/details/26005267

我还没理解透事实上o(╯□╰)o

//#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <iomanip>
#include <cmath>
#include <map>
#include <set>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdout)
const ll ll_INF = ((ull)(-1))>>1;
//const double EPS = 1e-8;
const double pi = acos(-1.0);
const int INF = 100000000;

double p[11];

void init()
{
    p[0]=0;
    for(int i=1;i<=10;i++)
        p[i]=1+1.0/i;
    /////////////
    for(int i=0;i<11;i++)
        cout << "i= " << i << "  " << p[i] << endl;
}

const double EPS = 1e-9;///

int main()
{
    //IN("hdu4803.txt");
    int x,y;
    //init();

    while(~scanf("%d%d",&x,&y))
    {
        if(x>y){puts("-1");continue;}
        double k=(1.0*y+1-EPS)/x;
        int cnt=x-1;
        double ty=1;
        for(int i=1;i<=x;i++)
        {
            double t=i*k;
            int down=(int)(t-ty);
            ty+=down;
            cnt+=down;
            ty=ty*(i+1)/i;
        }
        printf("%d\n",cnt);

    }
    return 0;
}