Merkkijono

#include <iostream>
#include <string>

int main(int argc, char** argv)
{
	std::string input="",lastinput=""; std::cin>>input;
	char cur;
	while (true)
	{
		cur='\0';
		if (input.size()<=1) break;
		for (unsigned int i=0;i<input.size()-1;++i)
		{
			if ((input[i]==input[i+1])||(input[i]==cur))
			{
				cur=input[i];
				input.erase(i,2);
				while (input[i]==cur)
					input.erase(i,1);
				break;
			}
		}
		if (input==lastinput) break;
		lastinput=input;
	}
	std::cout<<input<<std::endl;
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED