Given a positive integer, print the next smallest and the next largest number that have the same number of 1 bits in their binary representation.

CareerCup5.3.cpp

#include <iostream>
#include <bitset>

int GetNextLargest(int num);

int GetNextSmallest(int num);

int main()
{
  int num;
	std::cin>>num;
	std::cout<<GetNextLargest(num)<<std::endl;
	std::cout<<GetNextSmallest(num)<<std::endl;
}

int GetNextLargest(int num)
{
	using namespace std;
	bitset<32> btnum(num);
	bitset<32> btres(num);
	int highpos=-1;
	int pos=0;
	while(pos<31)
	{
		if(btres.test(pos)&&!btres.test(pos+1))
		{
			btres.set(pos+1);
			btres.reset(pos);
			highpos=pos;
			break;
		}
		pos++;
	}
	if(highpos!=-1)
	{
		//count the number of 1 from 0 to pos
		int count=0;
		for(int i=0;i<highpos;i++)
		{
			if(btres.test(i))
			{
				count++;
			}
		}
		//set 1s to rightmost
		for(int i=0;i<highpos;i++)
		{
			if(count!=0)
			{
				btres.set(i);
				count--;
			}
			else
			{
				btres.reset(i);
			}
		}
		return (int)(btres.to_ulong());
	}
}

int GetNextSmallest(int num)
{
	using namespace std;
	bitset<32> btnum(num);
	bitset<32> btres(num);
	int highpos=-1;
	int pos=0;
	while(pos<31)
	{
		if(btres.test(pos+1)&&!btres.test(pos))
		{
			btres.set(pos);
			btres.reset(pos+1);
			highpos=pos;
			break;
		}
		pos++;
	}
	if(highpos!=-1)
	{
		//count the number of 1 from 0 to pos
		int count=0;
		for(int i=0;i<highpos;i++)
		{
			if(btres.test(i))
			{
				count++;
			}
		}
		//set 1s to rightmost
		for(int i=highpos-1;i>=0;i--)
		{
			if(count!=0)
			{
				btres.set(i);
				count--;
			}
			else
			{
				btres.reset(i);
			}
		}
		return (int)(btres.to_ulong());
	}
}