reverse-bits.cpp

// Time:  O(32)
// Space: O(1)

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;
    }
};

// Time:  O(logn) = O(32)
// Space: O(1)
class Solution2 {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t result = 0;
        int count = 32;
        while (count--) {
            result <<= 1;
            result |= n & 1;
            n >>= 1;
        }
        return result;
    }
};