Merkkijono

#include <iostream>
#include <vector>
#include <math.h>
#include <string>
#include <map>
 
using namespace std;
 
string foo(string str) {
    int streak = 1;
    for (int i = 0; i < int(str.size());)
    {
        //cout << "i: " << i << '\n';
        if (str[i] != str[i+1] && streak > 1) {
            str.erase(i-streak+1, streak);
            i = i - streak;
            streak = 1;
            //cout << "after erase: " << str << '\n';
        } else if (str[i] == str[i+1]) {
            streak++;
            i++;
            //cout << "streak: " << streak << '\n';
        } else {
            i++;
        }
    }
    return str;
}
 
int main() {
    string str;
    cin >> str;
    cout << foo(str) << '\n';
    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