leetcode:190 Reverse Bits－每日編程第三十二題

Reverse Bits

Total Accepted: 46760 Total Submissions: 160246 Difficulty: Easy

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：

分塊交換，對於8位數，abcdefgh->efghabcd->ghefcdab->hgfedcba。對於32位，同理。

<span style="font-size:14px;">class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        n=(n<<16)|(n>>16);
        n=(((n&0x00ff00ff)<<8)|((n&0xff00ff00)>>8));
        n=(((n&0xf0f0f0f0)>>4)|((n&0x0f0f0f0f)<<4));
        n=(((n&0x33333333)<<2)|((n&0xcccccccc)>>2));
        n=(((n&0x55555555)<<1)|((n&0xaaaaaaaa)>>1));
        return n;
    }
};</span>