面试题-----按位翻转32位unsigned

// test.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"

#include <iostream>
#include <stdio.h>
using namespace std;

//方法一是将结果保存在了另一个变量中，从a中取依次取最低位，放入放入ret的低位然后右移ret
int reverse(int a)
{
    int ret= 0;
    for(int i= 0;i<32;i++)
    {
        ret = ret<<1;
        ret = ret|(a&1);
        a = a>>1;
    }
    return ret;
}
//方法二是交换a的低位和高位，首先取低位和高位，然后用异或判断高位和低位是否相同，如果相同
//则不变，如果不同则高位和低位分别取反（利用异或上1）
int reverse2(int a)
{
    unsigned int lowbit = 0;
    unsigned int highbit = 0;
    unsigned int low = 0x00000001;
    unsigned int high = 0x80000000;

    for(int i = 0;i < 16;i++)
    {
        lowbit = a & low;
        lowbit = lowbit >> i;

        highbit = a & high;
        highbit = highbit >> (31 - i);

        if(highbit ^ lowbit) //说明高位和低位不同，否则高位和低位相同则不用交换
        {
            int or = 1;
            a = a ^ (or << i); //低位取反
            a = a ^ (or << (31 - i));//高位取反
        }

        low = low << 1;
        high = high >> 1;
    }
    return a;
}

int main()
{
    unsigned int a = 0x01020304;
    printf("按位翻转后结果为：%d\n",reverse(a));
    printf("按位翻转后结果为：%d\n",reverse2(a));

}