题解 | 求int型正整数在内存中存储时1的个数

n = int(input())

# Write a function that convert the input number 
# from decimal to binary.

def dec_to_bin(num):
    # First, if the input number is 0, return 0
    if num == 0:
        return str(0)
    """Understand the core idea of decimal to binary conversion:
       Repeatedly perform floor division on the input decimal number  
       until the quotient reaches 0, while adding the remainder 
       (0 or 1) to each digit from right to left.
    """
    # Hence, the next step is write a WHILE loop that terminates
    # once the resultant quotient of the repeated floor division  
    # reaches zero.
    num_bin = ''
    while num > 0:
        num_bin = str(num%2) + num_bin # Add the remainder of the division 2
        num = num // 2 # Repeat floor division by 2
    return num_bin # Note: the output is a string!!
    
bin_output = dec_to_bin(n)

one_count = 0
for char in bin_output:
    if char == '1': # Each char is a string!!
        one_count += 1

print(one_count)