Reverse Bits

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).

通用方法

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t reverse = 0;

        for(int i = 0 ; i < 32; i++){
            reverse = reverse<<1 | ((n>>i)&1);
        }

        return reverse;
    }
};

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        n = (n >>16) |(n << 16);
        n = ((n & 0xff00ff00) >>8)|((n & 0x00ff00ff) <<8);
        n = ((n & 0xf0f0f0f0) >> 4) | ((n & 0x0f0f0f0f) << 4);
        n = ((n & 0xcccccccc) >> 2) | ((n & 0x33333333) << 2);
        n = ((n & 0xaaaaaaaa) >> 1) | ((n & 0x55555555) << 1);
        return n;
    }
};

n = (n >>16) |(n << 16); 这步完成的是将n的高16位和低16位交换

n = ((n & 0xff00ff00) >>8)|((n & 0x00ff00ff) <<8);

这步完成的是将n的每8位互换

上述过程为:

abcdefgh -> efghabcd -> ghefcdab -> hgfedcba