nyoj412 Same binary weight （位运算）

 

Same binary weight

时间限制：300 ms  |  内存限制：65535 KB

难度：3

 

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

分析：把n转换成二进制，找到第一个为 1 的位置p1（x&-x），从该位置开始再找第一个为 0 的位置p2，统计从p1位置到p2位置 1 的个数 c，然后把位置p2的0转换为1，最后把c-1个 1 加到最低位。

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
    int n;
    while(cin>>n)
    {
        int t,t1,t2;
        t=n;
        int tt=n&-n;
        if(t==tt)  
        {
            n=n<<1;
            cout<<n<<endl;continue;
        }
        int c=0,s=0;
        while(t)
        {
            t1=t&-t;
            t=t-t1;
            t2=t&-t;
            c++;s+=t1;
            if(t2>2*t1)
            {
                t1=t1<<1;
                n=n-s+t1+pow(2,c-1)-1;
                break;
            }
        }
        if(t==0)n=(t1<<1)+pow(2,c-1)-1;
        cout<<n<<endl;
    }
    return 0;
}