Reverse Bits

uint32_t reverseBits(uint32_t n) {
    long output = 0;
    int count = 0;            //记录第几位
    while(n)
    {
        while(pow(2.0, count) <= n)    //找到不大于n的最大count
            count++;
        output += pow(2.0, 32 - count);    //当pow(2.0, count) > n时，count需要减一才是目标count
        n -= pow(2.0, count - 1);        //因为要反转，所以31 - (count - 1)
        count = 0;
    }
    return output;
}

uint32_t reverseBits(uint32_t n) {
    unsigned int answer;
    unsigned int i;
    
    answer = 0;
    
    /*把一个unsigned int 数字1一直左移，直到它变成全0的时候，也就得到了该机器内unsigned int的长度*/
    for (i = 1; i != 0; i <<= 1)
    {
        answer <<= 1;
        if (n & 1)  { answer |= 1; }  //如果n & 1不是0的话才把answer的最后位置1
        n >>= 1;
    }
    
    return answer;
}