用python写算法5[二进制中1的个数]

题目：输入一个整数，求该整数的二进制表达中有多少个1。例如输入10，由于其二进制表示为1010，有两个1，因此输出2

解法:

#!/usr/bin/python

def NumberOf1(n):
    count = 0

    while n:
        if n & 1:
            count += 1

        n = n >> 1

    return count

def NunberOf1A(n):
    count = 0

    while n:
        count += 1
        n = (n-1) & n

    return count

# different from c, it won't stop correctly
def NumberOf1B(n):
    count = 0

    flag = 1

    while flag:
        if n & flag:
            count += 1

        flag = flag << 1

    return count

def main():
    number = 9
    print NumberOf1(number)

    print NunberOf1A(number)

    print NumberOf1B(number)    

if __name__ == '__main__':
    main()