cf C. Counting Kangaroos is Fun

http://codeforces.com/contest/373/problem/C

贪心，先排序，然后从n/2位置倒着找每一个可不可以放到别的袋鼠内。

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 5000001
using namespace std;

int a[maxn];
bool vis[maxn];
int n;

int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        memset(vis,false,sizeof(vis));
        for(int i=0; i<n; i++)
        {
            scanf("%d",&a[i]);
        }
        sort(a,a+n);
        int j=n-1;
        int ans=0;
        for(int i=n/2-1; i>=0; i--)
        {
            if(a[j]>=2*a[i])
            {
                j--;
                ans++;
            }
        }
        printf("%d
",n-ans);
    }
    return 0;
}