HDOJ1009

 

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<iostream>
#include<string.h>
#define inf 0x3f3f3f
using namespace std;
int f[100000],j[100000],x,n,m;
bool vis[100000];
double ans,maxx,b[100000];
int pattion(int p,int r,double a[])
{
    int y,z,ex2;
    double x,ex1;
    x = a[p];
    y = p-1;
    z = r+1;
    while(1)
    {
        y++;
        while(a[y] < x)
          y++;
        z--;
        while(a[z] > x)
          z--;
        if(y < z)
        {
            ex1 = a[y];
            a[y] = a[z];
            a[z] = ex1;
            ex2 = f[y];
            f[y] = f[z];
            f[z] = ex2;
            ex2 = j[y];
            j[y] = j[z];
            j[z] = ex2;

        }
        else return z;
    }

}
void quicksort(int p,int r,double a[])
{
    int q;
    if(p < r)
    {
        q = pattion(p,r,a);
        quicksort(p,q,a);
        quicksort(q+1,r,a);
    }
}
int main()
{
    while(scanf("%d%d",&m,&n) && m != -1)
    {
        for(int i = 1 ; i <= n ; i++)
        {
            scanf("%d%d",&f[i],&j[i]);
            b[i] = 1.0*f[i]/j[i];
        }
        quicksort(1,n,b);
        ans = 0;
        for(int i = n ; i >= 1 ; i--)
        {
            if(m >= j[i])
            {
                ans = ans + f[i];
                m -= j[i];
            }
            else
            {
                ans += 1.0*m*f[i]/j[i];
                break;
            }
        }
        printf("%.3lf\n",ans);
    }
}

部分背包问题,所以可以贪心处理,第一次超时了,后来用了快排先排序F[i]/J[i],从大到小找，酱紫就OK了