Codeforces Round #219 (Div. 1), problem: (A) Counting Kangaroos is Fun solution

Codeforces Round #219 (Div. 1), problem: (A) Counting Kangaroos is Fun: http://codeforces.com/problemset/problem/372/A

Codeforces Round #219 (Div. 1), problem: (A) Counting Kangaroos is Fun editorial: http://codeforces.com/blog/entry/9944

Codeforces Round #219 (Div. 1), problem: (A) Counting Kangaroos is Fun solution: http://ideone.com/RJ0rBv

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

int main() {
    int n, a[500005], cnt=0, b[500005]={0}, j;
    scanf("%d", &n), j=n/2-1;
    for(int i=0; i<n; i++) scanf("%d", &a[i]);
    sort(a, a+n);
    for(int i=n-1; i>=0; i--) if(b[i]==0) {
        while(a[j]>a[i]/2 && j>=0) j--;
        while(b[j]==1 && j>=0) j--;
        if(j<0) break;
        if(b[j]==0 && a[j]<=a[i]/2) b[i]=b[j]=1, cnt++;
    }
    printf("%d", n-cnt);
    return 0;
}