NYOJ 412 Same binary weight

描述

The binary weight of a positive  integer is the number of 1's in its binary representation.for example,the decmial number 1 has a binary weight of 1,and the decimal number 1717 (which is 11010110101 in binary) has a binary weight of 7.Give a positive integer N,return the smallest integer greater than N that has the same binary weight as N.N will be between 1 and 1000000000,inclusive,the result is guaranteed to fit in a signed 32-bit interget.

输入

   The input has multicases and each case contains a integer N.

输出

   For each case,output the smallest integer greater than N that has the same binary weight as N.

样例输入

1717
4
7
12
555555

样例输出

1718
8
11
17
555557

思路：先求N二进制表示最最左边出现1的位置i，再求在1出现后（即从i开始）最先出现的0的位置j，交换j跟j-1的值（俺考虑的加法），再将j-1后到i位置移到最低位即可，中间涉及位运算。

注：t&-t 的值  如下例:4=(100)--二进制 -4=（100）---（二进制）（补码） 4 &-4=（100）---（二进制）

#include <iostream>
using namespace std;
int main()
{
   unsigned int n;//无符号整数占4个字节（32位）
   while(cin>>n)
   {
      int t=n&-n;
      if(n==t)
      {
          cout<<(n<<1)<<endl;
          continue;
      }
      int i=0,j,high,low=0;
      while(((n>>i)&1)==0)++i;//1=i
          j=i;
      while(j<=31&&((n>>j)&1)==1)++j;//0=j+1  
       high=((n>>(j-1))<<(j-1))+(1<<(j-1));//高位
      if( j>=2)
         low =((n<<(33-j))>>(33-j+i));//低位
      cout<< high+low<<endl;
   }
return 0;
}