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).

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

思路

利用位操作，将掩码设定为0x80000000，利用左移操作，将每一位由高到低放入list中，再倒转。

在最后生成结果的时候也采用移位的方法，从list中取出每一位，并将结果进行叠加。

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class Solution:
    # @param n, an integer
    # @return an integer
    def reverseBits(self, n):
        res = []
        for i in range(32):
            tmp = n & 0x80000000
            tmp = tmp >> 31
            res.append(tmp)
            n = n << 1
        print res
        ans = 0
        for i in range(32):
            ans = ans << 1
            ans += res[31 - i]
        return ans