题目：

题解：

const uint32_t M1 = 0x55555555;  // 01010101010101010101010101010101
const uint32_t M2 = 0x33333333;  // 00110011001100110011001100110011
const uint32_t M4 = 0x0f0f0f0f;  // 00001111000011110000111100001111
const uint32_t M8 = 0x00ff00ff;  // 00000000111111110000000011111111

uint32_t reverseBits(uint32_t n) {
    n = n >> 1 & M1 | (n & M1) << 1;
    n = n >> 2 & M2 | (n & M2) << 2;
    n = n >> 4 & M4 | (n & M4) << 4;
    n = n >> 8 & M8 | (n & M8) << 8;
    return n >> 16 | n << 16;
}