LeetCode#190 Reverse Bits

Problem Definition:

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100),

return 964176192 (represented in binary as 00111001011110000010100101000000).

Solution : (很 Python)

def reverseBits(n):
    return int(((bin(n)[2:]).rjust(32,'0')[::-1]),2)

It can be expanded to:

def reverseBits(self,n):
    s=bin(n)[2:]
    s=s.rjust(32,'0')
    s=s[::-1]
    return int(s,2)

 然而这题真正的考点在于位运算

这里可以采用一种类似归并排序的思想（且称之为归并取反吧）

def reverseBits(self,n):
        n=((n & 0xAAAAAAAA)>>1)|((n & 0x55555555)<<1)
        n=((n & 0xCCCCCCCC)>>2)|((n & 0x33333333)<<2)
        n=((n & 0xF0F0F0F0)>>4)|((n & 0x0F0F0F0F)<<4)
        n=((n & 0xFF00FF00)>>8)|((n & 0x00FF00FF)<<8)
        n=((n & 0xFFFF0000)>>16)|((n & 0x0000FFFF)<<16)
        return n