添一道思科笔试题

sorock

编一函数 invert(int x, int p, int n) 使得整数x从第p位开始的n位反转。
最右边的位为第0位。不可以用循环！
比如x=1010011010001, p=4, n=4，运行函数之后
      x=1010000100001

dong_yoyo

反转？没看懂题目

guotie

too easy!

sorock

反转就是：0变1，1变0。

还请大虾指教！不要用循环哦！

[ 本帖最后由 sorock 于 2006-1-15 19:46 编辑 ]

zhhui2000

Maybe I am too fool,I think it isnot easy,it took me much time.

1. void main()
   
2. {
   
3.         unsigned int iDisp=0x14C1;
   
4.         short       int  p=4,n=4;
   
5. 
   
6.         printf("%0B\n",iDisp);     
   
7.         
   
8.         /*Maybe some complier hasnot the B option of  printf, then you can print it a decimal.*/
   
9. 
   
10.         iDisp = iDisp ^( (1<<(p+n)) -(1<<p) );
    
11. 
    
12.         printf("%0B\n",iDisp);
    
13. }

复制代码

[ 本帖最后由 zhhui2000 于 2006-1-15 22:11 编辑 ]

fwizard

异或

晏东

家里没gcc,我是用的TC编的，int 是16位。
位操作类型最好是unsigned
#include<stdio.h>
#include<string.h>

#define INT_LENGTH sizeof(int)*8
int invert(unsigned int x, int p, int n);
int main()
{
    printf("%x\n", invert(0x0f00, 4, 12));
    getch();
    exit(0);
}
int invert(unsigned int x, int p, int n)
{
    unsigned int temp = x;
    int left = INT_LENGTH - p - n;
    int right = p;

    temp <<= left;
    temp >>= left+right;
    temp <<= right;
    x -= temp;

    temp = ~temp;
    temp <<= left;
    temp >>= left+right;
    temp <<= right;
    x += temp;

    return x;
}

foolishfox

原帖由 zhhui2000 于 2006-1-15 20:39 发表
Maybe I am too fool,I think it isnot easy,it took me much time.

[code]void main()
{
        unsigned int iDisp=0x14C1;

        printf("%0B\n",iDisp);     
        
        /*May ...

呵呵,强人啊....................学习中.....................

wz_uestc

# include<iostream>
using namespace std;

int invert(int a,int p,int n)
{
        int nn=(1<<n)-1;
    int pp=nn<<p;
    int result=a^pp;
        return result;
}

int main()
{
        int a,p,n,t;
        cin>>a>>p>>n;
        t=invert(a,p,n);
        cout<<t;
        return 0;
}

sorock

The first solution, the best solution!