UVA 1346 - Songs

/*

    这是一个贪心的题目，要求求出最小的sum = b1+..+bn  ,bi= fi*(a1+..+ai);

假设以求出最小的sum  得到了最优序列 那么 bi+b[i+1] = fi*(a1+..ai) + fi+1*(a1+..+a[i+1])

sum1 = (a1+..ai-1)*(fi+f[i+1]) + f[i+1]*a[i+1]+ f[i+1]*a[i] + fi*ai;

现在交换 fi与fi+1  ai与ai+1 

sum2 = (a1+..ai-1)*(fi+f[i+1]) + f[i+1]*a[i+1]+ f[i]*a[i+1] + fi*ai;

ans = sum1 - sum2 = f[i+1]*a[i] - f[i]*a[i+1]

if ans > 0  : swap (i,i+1);

*/

#include<cstdio>

#include<cstring>
#include<cstdlib>


struct data
{
    int id;
    double l,f;
} a[80000];
int cmp(const void *a,const void *b)
{
    struct data *p = (struct data*)a;
    struct data *q = (struct data*)b;
    return q->f*p->l > p->f*q->l?1:-1;
}
int main()
{
    int n,s;
    while(scanf("%d",&n)==1)
    {
        for(int i = 0; i < n; i++)
        {
            scanf("%d%lf%lf",&a[i].id,&a[i].l,&a[i].f);
        }
        scanf("%d",&s);
        qsort(a,n,sizeof(a[0]),cmp);
        printf("%d\n",a[s-1].id);
    }
    return 0;
}