codeforces --- Round #250 (Div. 2) B. The Child and Set

#include<bits/stdc++.h>
#define MAX 100010
using namespace std;
struct Node
{
    int num;
    int id;
    bool vis=0;
};
Node node[MAX];
int sum,limit;
int lowbit(int x)
{
    return x&(-x);
}
bool cmp(Node a,Node b)
{
    return a.num<b.num;
}
int main()
{
    scanf("%d%d",&sum,&limit);
    int i,j;
    for(i=1;i<=limit;i++)
    {
        node[i].num=lowbit(i);
        node[i].id=i;
    }
    sort(node+1,node+1+limit,cmp);
    int cnt=0;
    for(i=limit;i>=1;i--)
    {
        if(node[i].num<=sum)
        {
            sum-=node[i].num;
            node[i].vis=1;
            cnt++;
        }
    }

    if(sum)
        printf("-1");
    else
    {
        printf("%d\n",cnt);
        for(i=limit;i>=1;i--)
        {
            if(node[i].vis)
            {
                printf("%d ",node[i].id);
            }
        }
    }
    putchar(10);
    return 0;
}