Pair exchange

Pairing exchange. Write a program to exchange the odd and even bits of an integer, using as few instructions as possible (that is, bit 0 and bit 1, bit 2 and bit 3, and so on).

Example 1:

•  Input: num = 2 (or 0b10)
•  Output 1 (or 0b01)

Example 2:

•  Input: num = 3
•  Output: 3

Sample code:

class Solution(object):
    def exchangeBits(self, num):
        """
        :type num: int
        :rtype: int
        """
        # return ((num & 0xaaaaaaaa) >> 1) ^ ((num & 0x55555555) << 1)
        #  与上面代码写的效果是一样的
        return ((num & 0xaaaaaaaa) >> 1) | ((num & 0x55555555) << 1)  


a = Solution()
b = a.exchangeBits(3)
print(b)

running result:

Problem-solving ideas

Regarding binary and bit operations: Take out the number at a specific position.

The odd-numbered bits can be manipulated first, and then the even-numbered bits can be manipulated.

• For odd-numbered bits, use 101010 (ie 0xAA) as a mask, extract the odd-numbered bits, and shift them one bit to the right;
• For even-numbered bits, use 010101 (that is, 0x55) as a mask, extract the even-numbered bits, and shift them one bit to the left.

step:

1. Take out the even digits and shift to the right by 1
2. Take out the odd-digit number and shift it to the left by 1
3. Sum or bitwise exclusive or