class Solution:
    def sortByBits(self, arr: List[int]) -> List[int]:
        def find_weight(num):
            weight = 0
            
            mask = 1
            while num:
                if num & mask:
                    weight += 1
                    num ^= mask
                
                mask <<= 1
                
            return weight
            
        arr.sort(key = lambda num: (find_weight(num), num))
        return arr