[leetcode] 190. Reverse Bits @ python

最新推荐文章于 2020-10-31 20:31:52 发布

原创最新推荐文章于 2020-10-31 20:31:52 发布 · 174 阅读

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本文介绍了一种方法，用于翻转一个给定的32位无符号整数的二进制表示，并将其转换回十进制整数。通过实例展示了输入输出的二进制字符串及其对应的十进制数值，解释了在不同编程语言中如何处理有符号和无符号整数的区别。

原题

Reverse bits of a given 32 bits unsigned integer.

Example 1:

Input: 00000010100101000001111010011100
Output: 00111001011110000010100101000000
Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.
Example 2:

Input: 11111111111111111111111111111101
Output: 10111111111111111111111111111111
Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10101111110010110010011101101001.

Note:

Note that in some languages such as Java, there is no unsigned integer type. In this case, both input and output will be given as signed integer type and should not affect your implementation, as the internal binary representation of the integer is the same whether it is signed or unsigned.
In Java, the compiler represents the signed integers using 2’s complement notation. Therefore, in Example 2 above the input represents the signed integer -3 and the output represents the signed integer -1073741825.

Follow up:

If this function is called many times, how would you optimize it?

解法

首先将n转化为32位二进制字符串, 使用format方法左边补零, 然后反转字符串, 转化为十进制整数

代码

class Solution:
    # @param n, an integer
    # @return an integer
    def reverseBits(self, n):
        bi = '{:0>32s}'.format(bin(n)[2:])
        return int(bi[::-1], 2)