Fancy number

fancynum.cxx

#include<iostream>
#include<cmath>
#include<string>
#include<set>
using std::endl;
using std::cout;

bool isFancyNum(int value)
{
	std::set<char> st = {'0','1','6','8','9'};
	std::string num = std::to_string(value);
	unsigned int len = num.length();
	for(int i = 0;i < len;++i)
	{
		if(!st.count(num[i]))
			return false;
	}
	if(len == 1)
		return true;
	else if(len & 1)   // len is odd number
	{
		int middle = len / 2;
		int begin = 0;
		int end = len - 1;
		for(;begin < middle;++begin)
		{
			if(num[begin] != num[end-begin] && abs(num[begin]-num[end-begin]) != 3)
				return false;
			--end;
		}
	}
	else   // len is even number
	{
		cout<<"len is even\n";
		int middle = len / 2;
		int begin = 0;
		int end = len - 1;
		for(;begin < middle;++begin)
		{
			if(num[begin] != num[end-begin] && abs(num[begin]-num[end-begin]) != 3)
				return false;
			--end;
		}
	}
	return true;
}

int main()
{
	int value;
	std::cin>>value;
	if(isFancyNum(value))
		cout<<"Is Fancy number.\n";
	else
		cout<<"Is not Fancy number.\n";
	return 0;
}