LeetCode#191 Number of 1 Bits

Problem Definition:

Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).

For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.

Solution:

　　基本方法，Python实现，直观到不好意思。

def hammingWeight(n):
    count=0
    count+=(n%2)
    b=n/2
    while b!=0:
        count+=(b%2)
        b=b/2
    return count

　　但是上面的代码不够“Python”，应该这么的：（reference1）(reference2)

def hammingWeight(n):
    return (bin(n)[2:]).count('1')

 　　然而用位操作是很方便的：

def hammingWeight(n):
        count=0
        count+=(n&1)
        b=n>>1
        while b!=0:
            count+=(b&1)
            b=b>>1
        return count

　　或者，这样：

def hammingWeight(n):
    n=((n & 0xAAAAAAAA)>>1)+(n & 0x55555555)
    n=((n & 0xCCCCCCCC)>>2)+(n & 0x33333333)
    n=((n & 0xF0F0F0F0)>>4)+(n & 0x0F0F0F0F)
    n=((n & 0xFF00FF00)>>8)+(n & 0x00FF00FF)
    n=((n & 0xFFFF0000)>>16)+(n & 0x0000FFFF)
    return n