437B - The Child and Set - CodeForces Solution

from collections import defaultdict, deque
from functools import lru_cache
from heapq import heappush, heappop
from bisect import bisect_right, bisect_left
from fractions import Fraction as frac
import math
hpop = heappop
hpush = heappush
MOD = 10**9 + 7

def solution():
    
        sum_, limit = map(int, input().split())
    first_bit_map = defaultdict(list) 
    for num in range(1, limit+1):
        first_bit = num & -num
        first_bit_map[first_bit].append(num)
    first_bits = list(sorted(first_bit_map.keys(), reverse=True))
    
    res = []
    i = 0
    while i < len(first_bits) and sum_:
        val = first_bits[i]

        if val > sum_ or len(first_bit_map[val]) == 0:
            i += 1
            continue

        sum_ -= val 
        p = first_bit_map[val].pop()
        res.append(p)

    if sum_ > 0:
        return print(-1)

    print(len(res))
    return print(" ".join(map(str, res)))
            
def main():
    t = 1
        for _ in range(t):
        solution() 
 
main()