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。

1 def hammingWeight(n):
2     count=0
3     count+=(n%2)
4     b=n/2
5     while b!=0:
6         count+=(b%2)
7         b=b/2
8     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：

1 def hammingWeight(n):
2         count=0
3         count+=(n&1)
4         b=n>>1
5         while b!=0:
6             count+=(b&1)
7             b=b>>1
8         return count

　　或者，这样：

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